I'm not saying that every SA:MP player will migrate to VC:MP if 0.4 is released, but you act as if the buggy state of the client has absolutely no correlation to the loss of players and the lack of enjoyability. You also act as if promotion will do absolutely nothing, therefore there is no point in trying.
News flash: people are still playing Vice City. They've bought the Steam versions, they've bought the mobile versions, and the more hardcore group probably still has their discs. They're not going to automatically know about VC:MP's existence, even if it would interest them. Some people might not even know they wanted it; it's basic marketing.
Maybe more scripters would also be attracted to VC:MP if it were more compatible with the features available in SA:MP (not entirely, but
more), but:
VCMP has maybe 100 functions if not less (wild guess), while SAMP has many more.
They probably still wouldn't play it if it crashed, lagged, and lacked in features, though. Nor would they be too enticed to play if they came on the forum and found its beta testers saying that it's pointless in going any further, that development is completely dead, and there is absolutely nothing that can be done.