Ok, let's see if I can piss off everybody at once. 
I'm stunned by the poll results. Chapel is a no-brainer at $2 and it would still be a great card at $3. Don't try to assess its objective cost or weep for your lost Chapel/Witch openings. Just compare Chapel to the reasonably-priced $3 cards. In Qvist's 2013 list, the median $3 card is Storeroom. Great! I promise never to buy Storeroom again. In exchange, whenever it shows up in the kingdom, I'm allowed to buy a $3 Chapel instead, ok?
I'm stunned that you're stunned. It's really *not* about how strong the card is. Indeed, lots of 5-costs are usually better than gold, silver is usually better than many-a-4-cost, Jack usually does more for you than counting house, etc. Cards aren't cost where they are because of power level directly. A card costs X because that makes the game best, and it makes the game best because of it costing X, not because it's better than cards costing less than X and worse than cards costing more than X. Now, power level is a very big factor here, but indirectly. The most pressing thing in the cost is when decks can reasonably expect to be able to buy the card. Obviously, to make the game interesting, better cards *tend* to need to cost more than worse ones, but this is a generalization, and not a hard-and-fast rule. Some cards, it matters how easy it is to amass large numbers of them. Sometimes, it's ow quickly you can get to them, or to a couple copies. Some cards are better costing more, a la remodel and border village, where the price can be an asset. With Chapel, you are almost certainly ever going to buy only one, and almost certainly just right at the beginning of the game. So making it cost 5 or more will be a big difference, because it takes time to get. But 2,3, or 4, you are going to be getting it on t1 or t2, if you get it, whether it costs 2 or 3 or 4. It actually doesn't really matter for the card itself, what matters is what you can get it with. And the issue here is 3/4 vs 5/2. At 3-4, a 5/2 player has to waste his 5 on it, and... well, not only would this forego a potentially powerful 5, but opening with the likely chapel/- is actually pretty unappetizing. This is pretty lopsided. If it's 2, then if there is a very nice 5 on the board for it AND there isn't something real nice on 4/3 open, then it can be big advantage for 5/2. It's not totally clear, but I think it's a better balance for 2-cost. Regardless, I am actually pretty dumbfounded that you think it should cost 3. This is the LEAST logical cost for it. At 3, the 4/3 player gets to get a 4 with it if he wants, putting Mr. 5/2 even further behind. So 4 is just a much better cost than 3. Also, in terms of power it doesn't make sense - Chapel would certainly be one of the best 4-costers.....
As to Donald's opinion on the matter, well... Donald is wrong, or at least he's missing the point. A $2 Chapel only makes the game more interesting because it balances out another questionable design decision: all the crap in your starting deck. If you want to make the game more interesting (i.e. faster and with a better chance for engines), just start with less crap. An underpriced Chapel gets you to the same place, but with a whole lot more shuffle luck.
Donald's general claim is wrong too. Most of the mis-priced cards are at least $1 off. I'd certainly still buy a $5 Tournament and pass on a $5 Adventurer. Plenty of cards could be made more reasonable by changing the price. The game would be better for it, too. The best kingdoms have a variety of playable cards and a range of reasonable strategies. The worst ones have a single dominating card and a bunch of overpriced/underpowered crap you just ignore.
Really? You've gone through lots of playtesting on these alternative versions, have you? The weak starting deck is necessary, because it gives you scope to make meaningful decisions over the long term, to plot out a course. Indeed, if anything, they should be *weaker*, not stronger. But they are probably good where they are now. If you can actually just have strong things up front, I think it would actually make *more* shuffle luck problems, not less, as well as exacerbate first turn advantage.
Tournament at $5 would not be a very good card in 2 player. Playable, sure, sorta similar to treasury. But this makes tournament a lot weaker, and not just because it is harder to get them or lots of them. At 5, it competes with lots of the cards which support it, making it pretty hard for you to get your tournaments AND stuff to help you connect therm. Sure, you can get lucky, but it won't happen all that much. And without draw help, it gets blocked a little more often than it connects even, and I am not sure it is even better than peddler. well, sometimes yes, but often I think not. And this would put it below all those peddler-with-a-bonuses, quite weak. And with more players it would just be terrible. You have to remember that this game was designed for 2 through 4 players, not just 1 vs 1s.
Adventurer at 5 might be okay. I in fact doubt it would be great, but it would certainly be reasonably playable decently often, a real option for BM decks. Probably this is one of the few places where I would say it would be better costed elsewhere, but you know, even this 5-6 isn't really a miscosting, just a potential difference.
Actually the only other cards I would look at changing price on, I think, are Rebuild to 6 and Ambassador to 4. Everything else almost has to be where it is (well, Scout, but man, they can't all be explorer). And maybe you can argue things shouldn't have been printed at all, and actually that's really where I would go with both scout and Rebuild, but it's not so bad anyway, and Donald has LOADS more playtesting experience here with other versions of stuff than I do, so I defer. Ambassador to 4 I think would be interesting for sure, as it takes a lot of the brutalest bite out, but on the other hand, it might just be too weak for multiplayer anyway.
Lots of games publish errata, revised editions, banned card lists, and alternative start/win conditions. Even Chess is a revised version of Shatranj. Dominion could benefit from a little revision too.
Well, banned cards, errata, revisions, fine, though it's obviously just much much better to not have to do this, and I don't really think there is a need.
Calling chess a revised version of Shatranj is bogus though. It's not like there were a well codified set of rules in Shatranj and then they were like 'huh, bishops should move further and not be able to jump' at a big conference meeting, and thus decreed it. No, people played with slightly different versions from place to place, and it naturally just sort of changed over time, and then eventually it was codified with the laws it has today. This is similar to the process of many card games (e.g. bridge, poker, various others) as well as sports. I mean, you wouldn't say that American Football is a revised version of Association Football (soccer). Or of Rugby even. And all these things are qualitatively different from Dominion as they developed over time, with slightly differing conditions, and this was a long slow process undertaken generally locally by players, whereas Dominion was something which was invented and polished. Now, Basketball fits more into that mold, and there are changes there as well, so it's not totally unreasonable to say you could have changes here. But it's undesirable for a card game like this to make cards which do things other than what they say as printed.
