Somewhere you said (and I paraphrase badly) that you could have made a 'complicated' expansion if you had wanted to. What did you mean by that: complicated in terms of number of processes/clarity of processes or complicated in terms of complex decision making in the turn (e.g. Remodel is more complex in this regard than Lab). Or some other form of complexity? Could you offer an example? 
I am talking about words, word complexity. Strategic complexity is fine. Simple ideas that take a lot of words, like Adventurer, are not as bad as complex ideas that take a lot of words, like Hermit, but they still add up to an intimidating package if there are a bunch of them.
Probably the most complex Dominion card is Tournament. It gives you a 2x2 grid of results to wrap your head around, then requires you to read 5 more unique cards to know what you're getting.
Let's consider three main set cards: Thief, Chancellor, Throne Room. Thief is the wordiest card in the main set, but what it does is straightforward and grokable. Chancellor is very simple but baffling. Throne Room looks straightforward but ends up creating rules questions. The problem isn't that I don't want sets full of Chancellors - though I don't - or Throne Rooms - though I don't. Those cards are problems but I do not have the problem of having tons of those cards lying around - they are rare. Instead the issue is that more and more of the possible cards to make (factoring in lots of stuff into that word "possible") end up wordy like Thief. While I tolerate a certain amount of that, especially for attacks (where the complexity is harder to avoid and the card is more important to the set), I sure don't want every card to be that wordy.
When you play Dominion, there are rules. Some are in the rulebook; some are on the cards. They are all in one place or the other; if I don't want a rule in the rulebook, it has to go on the cards, if I don't want it on the cards, it has to go in the rulebook. This seems straightforward. The general rule is, the number of cards you can make for a game is proportional to the product of the complexity of the game, and the amount of space you allow yourself for card text. The rules have to go somewhere.
You can obviously make Dominion cards for forever, if you don't hem yourself in with restrictions. The example I always used for Magic was, you could make the Scrabble expansion. It's all about anagramming. The game however has some serious restrictions. Aside from stuff like, no-one wants Dominion: The Catapult, the main audience for the game does not want it to be too complex. And they like that nearly everything is on the cards rather than in the rulebook.
I have already done the experiment of making an expansion after it was time to stop; that expansion is Guilds. It has a new mechanic that requires reading the rulebook to understand. As a result of moving rules for those cards to the rulebook, the cards themselves are sleek and simple, except Butcher. There is another mechanic that does not really require the rulebook. Those cards all have two abilities and are complex, except Masterpiece. Then there is an attack that's extremely wordy and does multiple things, and then three innocent cards that never hurt anyone, although if I had it to do again I would drop the "they only draw if they got cursed" bit from Soothsayer (a minor example of how I went too far trying to squeeze playability out of later cards).
I remain pleased with Guilds, although it will be surely be the expansion that sells the worst (we already have enough expansions, some foreign publishers will have stopped before this, it's small and people like those less, later expansions are more complex and people like that less). But uh I think it's there in my analysis: it's some fun new cards, where the complexity went into the rulebook for some cards and on the cards for others, and both add up to the game being more complex.
As long as the expansions are good, there will always be an audience of some size for them, even if they are overly complex. But Dominion gets played by gamer's spouses and gamer's parents and gamer's kids. It is so successful because it is not just for gamers. So I think it only makes sense that Dominion products try to be good for that audience, the actual bulk of people playing.
P.S. Without wanting to rake over first player advantage again, have you seen the hearthstone 'Coin' Card mechanic (which, although not without problems, does lead to a near 50/50 1st player/2nd player win rate, but perhaps more importantly, is an interesting mechanic). Anything you could see with a similar methodology applying to Dominion?
I haven't looked at Hearthstone; I know it's some kind of online Magic Lite. I am not unhappy with where things stand for first player advantage in Dominion. There are boards where a very minor compensating advantage for the 2nd player would still be too much - including, for example, half a VP.
