This looks worse than Bridge. If you use the two Buys Bridge is +1 Buy +$3 but Bridge provides a Coin token in advance.
Despite the ability to save this for later the megaturn potential is actually lower as you need the extra Buys from another card. This is why I'd put the extra Buy on the calling part.
That's a good comparison. If you call it the same turn you play it, then you get the same benefit as a single Bridge, which is a good sign for a $4 card.
If you don't, then you need to play something later to be able to bring all your reserved wine critics back for your megaturn. Another wine critic will do. In some ways, this is stronger than a bridge, because although two bridges can be +2 Buy +$6, you can't achieve that without a third support card; whereas you can get +1 Buy +$6 with just two wine critics.
If it gave the +Buy on call, you could trigger it whenever you wanted by buying a copper, and you'd get +N buys into the bargain, which seems overly strong to me.