Buying coppers is still pretty lousy without a good reason.
Let's say go BM/Smithy&Copper. You pile all the duchies, estates, and Smithies. You walk away with 8*3+8+3 = 27 VP. You need a minimum of 16 turns to end the game. I use Moneylender to thin down to an engine and build to silver x4/village/Smithy. I burn 8 VP on the silvers and then need just 6 provinces to win (6*6 - 8 + 3). In a 20 turn game that is pretty easy.
But could you not build an engine of coppers & draw? Why yes you could. But how many turns behind would you be? Say we have Hunting grounds, Rc, and Hamlet for our deck. Getting to $6 off coppers is impossible, so advantage to take the 4 VP hit and get on to the big stuff. Say we use Catacombs (no trashing) instead. Well even if you open C/C, you still have a 1/4 chance of hitting an estate each card so it will be a good number of turns before your first $5 most of the time, let alone your second.
And think about it, if you can build a one province engine a turn sooner, you are looking at a 3VP swing and perhaps as high as 12 VP for getting their a turn first. In the latter case, it is totally worth it to buy up to 6 big treasures - or something like Silver x2, Gold x4 and just play the normal $16 engine game. Getting to provinces a whole shuffle later is typically a pretty huge VP swing that makes opening double silver trivial in comparison.
Or think about it this way. How often is it worth it to buy Silver over Monument? As an opener you forfeit 1 VP on the first shuffle and normally at least 1 VP more ... and that is for something that merely takes up a terminal instead of hurting your odds of hitting $5.
Yes worry about the relative number of Golds & Silvers. Yes limit your BM games, declare silver flooding DOA, and enjoy copper based setups (engine or slog) ... but be very wary of letting 2 VP slow you down. Buy the thing that lets you hit your key price point sooner; there is time later to buy VP.
More interesting are the questions of exactly how much treasure you should buy. I do suspect that Bandit Fort pushes you more towards singleton province engines - going from $8 to $16 is at least -6 VP (assuming copper/something else is not supported on the board) and it delays you a turn. Or in other words by building up to 2 provinces per turn, you start buying provinces at least a turn later and need to buy at least one more. Ceteris parabis the VP would then go something like -6 (end of your turn), -12 (end of theirs), 0, -6, 6, 0, 6 for a win ... but that meant you could gain silver, gold, gold in one turn. Anything less quick than that is a net loss.
Also fun is that at some point, you will want to trash out and just pile duchies. When that point comes in a game, I cannot say, but it will be fun to find out.