After that probably unhelpful dissertation, my question is: does giving bonuses on "overpaying actions" overbuff Village Idiot decks?
Village Idiot decks are bad not because you end up with too many unused actions but because of the opportunity cost of all those Villages. For every unnecessary Village you buy, you could have had a Silver or strong $3 card instead. If you buy too many $4 and $5 Villages, you're depriving yourselves of the Smithies, Council Rooms, Attack cards, etc that you need to make your engine work better than that of your opponent(s).
The 'overpaying actions' card you're thinking of exists as Diadem, the Prize from Cornucopia. I rarely find a use for it, not least because the race for Provinces in a Tournament game makes it harder to build the engine that would make Diadem work, even if they are in the kingdom. Diadem is usually the 4th or 5th best Prize (after Followers, Trusty Steed, and Princess, not necessarily in that order), and often you'll want Duchy by the point in the game that Diadem becomes the best Prize left.
Think about it: Diadem basically turns your basic Villages into Bazaars (turning the leftover +1 action into $1). That's nice--but a deck full of Bazaars won't win you the game, even if Bazaar is itself a decent card.
I don't want to be harsh, but before you think propose more fan cards, you should look over the Wiki and see what real cards have been made (or play on Goko and see for yourself how these cards work). Most of your ideas are already in use in the other expansions.
