Re: Watchtower: depends on who you're playing with. People here know all about the gainers synergy, particularly university (which is a very tasty combo). Is it underrated? Surely, by some people. The question is what group of people you're talking about.
I would say the defensive powers are probably a little bit underrated - you can chain watchtowers to keep yourself fairly well defended in some circumstances, but in general, the card isn't really.
60% of the cost of library is not something you want to use. Costs don't scale linearly, really almost at all. You at least have to note that they each cost 1 buy/gain apiece, but that the $$ cost is more about a limitation on when you can get them than anything else.
One thing to note about draw-to-x cards in general is that they are not all that great for engine building. (Ducks). Yes, you can make an engine with them, but the thing is that it's harder to chain them to get full benefit. If I have a 5 card hand, Watchtower draws me 2 cards. But if I've already played one, then I am going to need to play some other actions to get any draw power from the second. This sometimes means disappearing villages (or those rare non-draw non-terminals like lighthouse), but very often it means playing some non-draw terminals. And then to not draw things dead, you basically need to have more villages than you otherwise would, plus you have less choice over the priority you play your other cards in.
This is actually a pretty significant drawback.