Blair's contract doesn't end before 2013, so this isn't a cap space issue this summer.
assuming Amir Johnson can only be acquired with the Bonner contract, the cap implication for 2012 isn't that dramatic as well. he eats 2.4 million cap space compared to the situation before the trade. considering we won't get a premium FA and would need to overpay a player of Amir's level to come here anyhow, this isn't a bad deal as well.
just a guess: Spurs do the trade, amnesty RJ, re sign Tim for 8, bring in Lorbek for 3 per, this still leaves about 3-4 million for another FA.
Tim-Tiago-Lorbek-Johnson-Blair looks like a high quality front court rotation. much better than what we currently have.
so yes, I would do it.