It is relatively easy to justify signing Kobe, just hard to do. It is not easy to justify signing anyone else so I guess the Suns can plan on going into next season with the same crew as last season.
I can't comment on whether the Suns would lose these guys to other teams who will offer them less money, but over the years the Suns have had good luck at getting guy like Manning, Rogers, Delk, Chapman, etc. to sign on.
Is Barry old? At 32 I suppose he is older than might be optimal, but he is still a quality defender and a fantastic shooter. He can play point guard as well as playing off the ball, he is tall enough to defend SG's and still do a decent job on PG's. Even when he doesn't shoot, he forces opponents to play him tight which would open up more opportunities for the JJ, Shawn, and Amare.
Blount is not a top center and would not be paid like one either. Once he was given a chance, he proved to be better than expected on offense while being a solid defensive/rebounder type big man.
Maybe sitting on the cap space is the best move, but I don't see any straight free agent signings that would solve the Suns problems better than Barry and Blount. Nash and Okur? Yeech. No defense.
Do Barry and Blount give the Suns an instant championship team? No. Neither does Kobe. The current Suns have to get a lot better for this team to be a championship level team. Amare has to make the next couple of steps, JJ has to keep growing, Shawn has to become a better on the ball defender and smarter shooter, and Lampe has to become an NBA center. No signing is going to speed that process up, but it could make the team better both now and in the future.