Shelters are meant to be weak, hardly better than Estates (and sometimes worse). I think Lost Garden would be OK as "1 VP for every 2 Curses, Shelters and Ruins in the deck". As Asper pointed out, the current wording would exclude everything except Curses and Hovels... although it is actually ambiguous, in that you can read them as separate categories (e.g. Copper and Province count because they are non-Actions, Village counts because it is a non-Treasure).
Not sure about Townstreet. Consider this background on Hovel:
Hovel is the only one that changed. Originally it was an action you could trash by discarding your hand. It turned out that trashing it turn 1-2 usually seemed like the correct play, even if you drew it with four Coppers. So that was no good. Hovel as printed has nice flavor going for it; you move out of your old Hovel and into a nice Duchy.
Townstreet is a card that essentially auto-trashes itself every time. It might still be OK in that it doesn't just remove one of your first two buys, and the single +Buy does tempt you into calling it once in a while. Still, something to be wary of.
Crypt -- Only trashing cards in play doesn't weaken it that much. In fact, it makes it a
stronger Copper trasher than other options (now that it triggers at the end of your Buy phase) because you already got the +$1 from playing Copper. This is actually really strong for a Shelter and it changes the game a
lot more than any other Shelter, even compared to your other ones. That said, I think it's still OK as long as you don't mind the Shelter having that much impact. Being terminal helps temper it as well.
The on-trash effect feels superfluous to me. The Copper trashing is already very significant, and the fact that it can trash itself afterwards is icing on the cake. Gaining a useful card afterwards is way overkill for a Shelter.
It doesn't help that the effect needs some awkward wording. Note that specifying Necropolis doesn't actually work as you intend. When a card says "gain", it means from the Supply by default. Otherwise, it has to specify -- e.g. Urchin says "from the Mercenary pile", Marauder says "from the Spoils pile". So how do you reference gaining a Necropolis? It's not in the Supply and it doesn't have a pile to reference. Either you'll have to be inconsistent with official wording or you'll have to do something awkward. The ambiguous definition of "village" doesn't help either.
Overall, the card is plenty interesting (maybe even too interesting!)
without the on-trash effect. Just trim the fat.
For something similar to the on-trash effect that is more clearly worded, you could have another Shelter like this:
Decrepit Village
$1 - Action-Shelter
If this is not your first or second turn,
+1 Card
+2 Actions
Discard a card.
(or some other weak village effect.)
PPE:
Ruins are Actions. All Shelters except Hovel (including yours) are Action or Victory cards.
Thanks for pointing out another elementary mistake. So the card should read "Shelters, Ruins and Curse" instead of "non-...".
I think that it is too weak if it does not start out with a VP value of 3 and that the other idea which has been suggested (or misread because of the 1/2 thingy) of 2 VP per Curse, converting them into Estates might be too strong. Not too strong in terms of preventing players from buying Cursers (if there would be a card which handed out Estates it would probably be a weak junker but still a junker unless there is Silk Road or Gardens) but too strong in terms of making the decision of whether to trash Lost Garden or not easier.
It's really not too strong. Again, Shelter should be compared to Estate, so a VP value of 3 is already too high.