As I was saying in another thread, adding complicated wording just to stop you from doing something rare and cool does two bad things at once. Why NOT allow this trick? It's only possible when both cards are in the same game, which would be a minority of games with either card, and even then can't activate the combo without drawing two Tacticians AND Ghost Town in the same hand. That's a non-trivial amount of money to spend to get the cards, and a non-trivial amount of work to line them up properly. Seems to me you ought to be able to do it.
Crazier things are possible: Golems + 1 Counting House + Tunnels? Any number of KC-Scheme tricks?
You're right that multiple tacticians in one turn would be hard to pull off. Essentially you'd have to play your tact, and then draw another one somehow with only your set-aside ghost towns to start you off. This would be very hard to do without a +cards card to potentially draw to. And it would probably be optimal to just play this as more of a single tact (or single tact per turn), unless some serious trashing occurs. And you still need to buy treasure cards to have any buying power.
I divided the 17 cards that Ghost Town would affect into 4 categories, based on estimated impact they'd have when paired with GT. (Note: All percentages are based on there being Ghost Town + 162 kingdom cards available (which is base + all current expansions + promo).
Tier 1 (probability of a Ghost Town game including one or more Tier 1 cards: 15.85%)
Tier 2 (probability of GT game including one or more Tier 1 or Tier 2 cards: 41.02%)
Tier 3 (probability of GT game including one or more cards Tier 3 or better: 53.83%)
Jack of All Trades
(Note: I debated including Jack in Tier 2 but I think the silvers can get in the way of a Jack engine which isn't that good in the first place since it only draws to 5 cards anyway.)
Tier 4 (probability of GT game including one or more cards Tier 4 or better: 64.11%)
That seems to be a pretty good level of interactivity. And it would mean that in approximately 50% of games Ghost Town would be better than the other four $4 villages (Farming Village, Mining Village, Walled Village, Worker's Village), and in 50% of games it would not. Making it of relatively equal value overall.
I think the final phrasing would be: "When you draw this card, you may set it aside. At any time during your action phase, you may return it to your hand. Discard any unreturned Ghost Towns during your clean-up phase."