BB charizard is a real gem for Great/Ultra league PvP.
In PvE, the BB zard will always be better than a non BB zard.
Should you power it up? Depends, do you have enough Moltres/Entei to put together a team of 6? If so, the BB zard isn't worth powering up. If not... Wait until fire is an in demand attacking type to power up the BB zard (because fire doesn't do anything on offense right now).