If Ainge chooses a guard, it's a signal he has a deal in place to trade a guard. Whether it's the guard he's drafting or another guard.
Whether it's worth doing depends on whom he gets in the trade--and whom he trades. Trading IT doesn't net improve the offense. Trading Bradley or Smart weakens the defense, so he better get some D back.
Maybe the best option is to draft a big who can score (Chriss?), or trade the #3 for a big who can score. That's where maybe Love fits, or even Okafor, or somebody like that. That adds a scorer without weakening their backcourt--their strongest suit. I should add that Okafor is a lot cheaper than Love. Also, it's a question of inside vs outside points.
Ideally, I think they want to strengthen their frontcourt without weakening their backcourt.