Stamp Collector -- I
think (but am not so sure) that Stamp Collector should cost $3. Compared to Village, there is a chance of whiffing when you only have one action in hand, but you make up for it with the possibility of giving more than +2 Actions. It's notable that this is equivalent to a cantrip+ because you will always get at least +1 action if you actually have an action in hand to play. OK, it's not quite a cantrip in certain edge cases (e.g. TR, Golem) but it's pretty much so. I think the possibility of whiffing is balanced by the potential for extra actions, so I think the cost should match Village at $3.
As for the function itself, I like it just fine. Simple, elegant, clear purpose in design. I suppose that there might be some potential abuse cases with Scrying Pool (SP deck chock full of powerful terminals and just a Stamp Collector or two to provide all the +action you need). Overall though, it looks good.
I see that Gendo says the same in much fewer words.
Almanac -- I think there may be some timing issues and redundancy in this card. You say you have the gain-to-bottom so that "you can't just spam almanacs with itself". I take this to mean that you don't want it to be easy to use Almanac to gain another Almanac, rinse and repeat. In this case, there is redundancy in that you have an on-gain bottom-deck as well as bottom-deck on the reaction's gaining ability itself. One should suffice. You can keep it as an on-gain to nerf gaining Almanacs in other ways while allowing the reaction to gain (for example) Silver without having to bottom-deck it. Or you could leave the bottom-decking on the reaction so that anything gained via reaction is bottom decked (which is not necessarily a nerf) while making Enlightenment itself a bit faster to activate.
As for the timing issue, there's a question about when the reaction actually triggers. "When you reshuffle your deck" -- does that means when you are actually shuffling it, or when you are about to shuffle? The former doesn't make sense because, if you are already shuffling, there is no longer a discard pile from which you can reveal Almanac. But if the latter, the timing is strange. Consider:
I am about to shuffle. I reveal an Almanac. I gain 2VP and I gain some card X. I now put X on the bottom of my deck. Since I am about to shuffle, my deck is empty, so the newly gained card is the ONLY card in my deck. Now I continue my reshuffle... wait, do I shuffle that single card in my deck with the rest?
The problem is more obvious if you have multiple Almanacs. If you try to think it through, it doesn't seem like it is possible to resolve more than one Almanac on a turn.
I believe I understand the intent (shuffle first, then put the gained card on the bottom) but it isn't correctly and unambiguously conveyed as currently worded. You could probably just be explicit about the timing:
"When you would reshuffle your deck... If you do, shuffle your deck, +2VP and..."
Granted, this could sound a bit awkward and redundant to players who don't pay attention to these little timing quirks. It also cements that you can only trigger one Almanac per reshuffle.
Oh, there is one other potential issue too -- IIRC, you are prohibited from looking through the discard and thus you can never actually reveal an Almanac from it. I think this is easily remedied by taking a cue from Counting House and maybe Duchess -- "[In games using this,] when you reshuffle your deck, you may look through your cards and reveal this from the discard pile..."
As for the effect itself... it actually seems a bit bland to me. Power wise, I don't know. If I am thinking about this correctly, Gendo is wrong that it can whiff on the second reshuffle (and likewise, I think you're wrong that it's dead for two shuffles). When you gain it, it goes on the bottom of your deck. In the best case scenario, you draw it as the fifth card in your hand just before the reshuffle and you don't even have the option to trigger the reshuffle during your turn. You discard it, then you reshuffle and you get to trigger the reaction on that first reshuffle.
The more common case would be that Almanac misses the reshuffle the first time through, but then you discard it and it's guaranteed to be in the discard pile when you reshuffle the second time. Either way, it's only a dead card in your hand once. Right? I'm not missing something here? Also, you don't have to buy it again because you can just gain another Almanac with it.
Anyway, it just doesn't seem very interesting to me. The mechanics feel clunky and overly complicated for no great reason. As Gendo notes, it kind of just fills the same niche that Monument does, except in a rather roundabout way.
Enlightenment -- As Gendo says, this is almost as brutal as Pillage, which is a one-shot $5 card. It hurts even more if you can play it twice in a turn, because you have it at "4 or more cards". Even when it starts hitting Provinces instead of key action cards or treasures, it still hurts because the dead card will be clogging you up again this shuffle. Yes, it's at the bottom of the deck so it will probably miss the next reshuffle, but that just means that you see the dead card again earlier than you otherwise might have.