The big thing with villa is that it changes your order of purchase.
Take something simple like Smithy/Alms. Opening Smithy/Smithy is pretty weak as 7/11 times you will collide Smithies and reduce buying power. With Villa, that becomes a pretty nice setup. Spend $4 (net $3) on Villa and purchase another $4 or $3.
Other double terminal setups become vastly better as openers and even in later turns, being +action deficient is vastly less costly than normal. Villa lets you buy terminals sooner. Either they do not collide & who cares or they do and you buy villa. Only when you cannot hit $4 or the pile runs out is being terminal heavy bad for Villa.
Pretty much any remotely viable double terminal opening (Workshop/Smithy, Remodel/Wt, Herm/Scav, Steward x2, Hag/Oracle) works exceedingly better with Villa on the board.
This should not surprise us, Dominion is generally well balanced and an action is worth a good bit; being able to mitigate the worst case scenarios with terminal collisions should fairly dramatically tip the decision towards too many terminals over too few.