Just because Q played no defense in the past doesn't mean he doesn't have the capacity to play d. We've got a history of bringing in players that were never known as defensive stoppers and turning them into respectable defenders. It's one thing we do well. So I doubt that would stop us from getting him.
Secondly, you probably didn't see him play when he was on the worst team in basketball at the time (Clippers) or you would know he's very capable of posting up smaller players and driving the ball. The Knicks brought him in to do more than just shoot threes like he did in Phoenix and were convinced that Larry could break him of the habit. Only, he didn't get enough consistent minutes because of fluctuating line-ups and injury. Oh and he wasn't very incosistent a couple years ago when he played for the Suns...he led the league in three pointers made.
As far as productivity, they are nearly identical for their careers (12ppg 4+rpg), it's just the short term memory of Bonzi having an insane playoff series and Q-Rich having an off year.
As far as his "bad back", I think it's a concern but hadn't heard much about it before it was quoted in the same article that mentioned him as trade bait. I'm not lobbying us to get Q-Rich, but I think he's a superior option to Bonzi and could be had for cheaper.