I think power isn't necessarily the issue here; not every card needs to be exactly as powerful as possible. With 'exactly', I think farmland still has the most important interactions (gold/farmland->province) but is a much more interesting card... what can I keep in hand to still end up with $6?
I think there's also a flavor thing, that trash-for-up-to-this-much-more is only for cards very close to remodel, while the weirder versions have 'exactly'.