Masterpiece is worth it, with the Smithy or without it.
Masterpiece isn't worth it, regardless of Smithy.
I remember clearly that Masterpiece+BM beats BM if you buy Masterpiece on $5 and $7 but Gold on $6, I think that was the optimization they found. Seeing that my opponent was going for something I didn't have confidence in makes my objective not to get 4 Provinces as quickly as possible, but rather to get 6 Provinces as quickly as possible. I think Masterpiece is better than Trading Post for that particular goal, but probably combining the two is best. All of this is in the absence of Smithy, which is probably better than Trading Post for Masterpiece+BM.
There's Procession-Armory and a spammable 5 cost... this game shouldn't last beyond T12. Trading Post is terrible because way too slow. With the self-sustaining top-decking you don't really need trashing. Just get a Procession, Armory and Highway each turn until your turns start to explode.
The self-sustaining top-decking is something I hadn't considered. You can play Procession+Armory every turn to top-deck Procession+Armory. This empties piles but it doesn't score points and I don't understand what you mean by "your turns start to explode."
It looks to me like you're using two of your five cards every turn, plus your action, to gain a Highway every turn, so you get to cycle three cards each turn and maybe buy something. Maybe with some Highways in your deck you can make that thing a Province but that doesn't seem reliable at all. There are no Villages or draw in the kingdom so Procession+Procession or Procession+Highway can kind of work but Processioning a Highway doesn't actually do anything and you still aren't drawing cards. You need extremely lucky pulls from the Black Market deck for anything spectacular to come up (that my feeble mind can think of) and where are you getting the actions to play that Black Market?
And T12 has to be a huge exaggeration for length of the game. Let's say you get perfect draws and manage to collide Procession+Armory on T5 in a deck with no trashing. You've now emptied piles on T15, but how do you expect to have more points than Big Money+nothing at that point? You've been having 3-card hands since T5 and you don't get to play any actions. Granted, you're getting a free Peddler (Highway) every turn, but I'm not convinced that this is worth it.