Back-up point is definitely a pretty big need, but I think a bigman is more so. Any PG we pick up likely won't see true minutes in the playoffs and will be an emergency back-up in case Gary Neal crashes and burns. Otherwise, he'll just eat up a few minutes in the remaining regular season games and maybe position himself for a bigger role next season (ie, Patty Mills).
Another bigman addition could very well push Blair out of the rotation completely and eat up big minutes not only in the regular season but also the playoffs.