shooting someone is also how VIG confirms his role and its not like TOWN will be better able to take that risk later.
The philosophy of when and how often a player should shoot is debatable. One school of thought is that kills narrow down the pool of suspects, so any player that is more likely to be scum than random should be fair game for being shot. This same school of thought favors killing on every Night, including Night 0 (when there is no game-related information about any player. The best play as a Vigilante is to shoot scum. This requires the Vig to find scum. There is no easy way to do this. However, because of their ability to make or break entire games depending on who they target, Vigs are frequently lauded and/or blamed for their decisions beyond appropriate proportions. Thus, as a Vig your best bet is to make decisions that will not cause you to be hated by every other player in the game. If in doubt, shoot a player that people would want to policy elimination (e.g. lurkers).
GP is certainly experienced enough to evaluate most likely scum and take that risk on behalf of TOWN, if GP is TOWN. I would say GP's best guess is at least as good or better than TOWN guess. My experience is that most DP1 VIG claims are false. I think TOWN should set the expectation that VIG takes a chance tonight or lose all cred from early claim.