The skatepark has been a great use of a derelict site, but surely the point is that that site should not have been allowed (and should not continue to be allowed) to have become derelict in the first place. As someone who couldn't live much closer to the Grove Tavern, I would welcome any redevelopment efforts. The current state of the pub is untenable, wasteful and ultimately an embarrassment for the local area.
The concerns mentioned about young people and the lack of public space for them to spend time are totally valid. And I agree, its very inspiring that a group of teenagers have built the skate park and created something out of nothing. But that shouldn't prevent the site being turned into something that is of utility to the whole community - whether that be housing, supermarkets or a pub/restaurant.