Any card that increases the play value of Silver is inherently going to be better with an engine than with BM.
Consider for example any "Silver produces an extra $1" version (call it "M") against a generic terminal silver ("T").
M vs T
0S => $0 vs $2
1S => $3 vs $4
2S => $6 vs $6
3S => $9 vs $8
4S => $12 vs $10
So in any situation where M is getting you a better result than T, then you could have bought a Province anyway. This makes the M effect very unexciting unless you have +buy and an increased hand size... and it's hard to get those without an engine.
Then naturally M has the same weakness that Coppersmith has, in that its effect is only really good in an engine, but the treasures needed to make it good tend to gum up engines, plus it occupies a kingdom pile that could have been a useful engine component. (That last point is why, in general, terminals that only give +$, like Harvest, tend to be worse in engines than you'd think. Occupying a kingdom pile is a big deal.) If M has trashing or +buy, then it has some utility in an engine apart from the +$.