Monument is always good, but you have to look at opportunity cost - both what else could you have bought, and especially in this case, what else could you have played - you're limited by hamlets. If you want to try for monument spam, you will need tributes, and you'll need this to be reliable, but... this seems awfully slow.
I would guess there's a place for monument, but it's a small window, and you need to be RIGHT on top of it, because as Shark_Bait points out, you aren't likely to have time to get a dozen monument plays to overcome 2 provinces, or even 9 and a duchy. Unless you're opponent is so far behind that it doesn't matter anyway. But a couple points, or maybe 4 to overcome a duchy, 7 if they dip for 2 duchies... again, if you time it absolutely right, which is extraordinarily tricky - I would probably mess it up.
Bishop has a weird interaction with watchtower, in that it helps you get handsize down, but them too. This probably makes it quite good late, but again you need to be able to play enough actions, and how many hamlets do you have, and if you have that many, how many spare bad cards to you have to trash. So only late, when you are trashing expensive things, which also limits your opponent's usefulness. Maybe the timing window is such that they supplant monument, actually, so there's another opportunity cost for you.