I think it could work, but I think the cost is too low. Would need play-testing to figure out how much higher the cost would need to be.
The fact that Town Hall could gain huge victory points without clogging a deck give it crazy potential for ridiculous turns. I think in Colony games, with more time to build a big engine, this would dominate over buying Colonies. Yes, at $16, Colony/Duchy is 13 pts vs. 12 pts from Town Hall, but C/D puts two dead cards in your deck. TH would keep your deck fluid, making it possible to stack 12+ VP turns without slowing down your deck.
Even if TH was offered as a pure Victory card (no actions, just the on-buy effect), I think it would still be worth $5 in many games. With that same $16, you'd likely take the TH vs the C/D, because for the difference of only one VP, you'd keep a second dead card out of your hand. In a Province game, the $16 would almost always go to the TH, since it would be the same points, but only one card in your hand.
Never mind the fact that the lack of need for +buy makes it easier to set up a viable engine in more kingdoms... If all I have is Village/Smithy (or variants), I don't need to worry about clogging my deck with woodcutter or herbalist, etc., for the +buy.
Even in a Province game, you'd have a lot more time than usual to set up a mega-engine, because you wouldn't need to worry as much about your opponent buying Provinces. Usually, every Province your opponent buys is a lost opportunity cost because if you get too far behind on points, it's mathematically impossible to catch up. With TH, you don't have to worry that your opponent just bought the 5th province... with extra time to build a bigger engine, a couple of mega-turns could overcome any Province-lead.
Totally a game-changing card. I think it's a great idea, but I suspect it's totally too-powerful as-is.
If you strip away the action part, it's still very powerful and a game-changer, but at least a lot closer to balanced.
Don't forget that with the coins in guilds, extra coins would suddenly double as Victory Points... you could save them for the huge-overpay turn and instantly convert every coin into a VP... even without +buy.
Seriously, some ridiculous possibilities, but fun to consider.