Remember, he'll be 29 by the time you get to use him in league games.
I believe that decline starts at 33, so you have 29, 30, 31 and 32 before he starts to show decline. 4 seasons isn't bad. I have no idea how fast the loss of skills is, but you probably could get another season out of him or sell him before he becomes worthless.
I guess it depends on long term plans and just how much money you're talking about.