Well, your point is fair. However, most of the free agents signing contracts now are restricted, so they would not have been accessible as such, regardless. I say we build through smart drafting and free agency.
The trade you offered is preposterous. We do not become a better team, while improving one of our (once) fiercest competitors significantly. If you would make that trade with the intent to improve for the future, I would argue that Ray Allen could obtain better future prospects, while not strengthening a competitor.
Ronnie Brewer is a decent defensive stopper ala Tony Allen. But, him in a combination with Rondo would, for the same reasons as TA and Rondo, would not be great. Neither are threats from three point range, and Brewer is not creative enough either.
Asik is a great defensive player, perhaps among the best Cs. But from my perspective, he's a great piece for the right team, and not a corner stone in any way. Resembles what Perkins did for this team, however, without a core of four studs, he would be exposed greatly (offensively).