Regarding Pro Bowl level WRS, how many maintain that level (let alone improve) when they move on to a new team? So much of their success is timing with the QB and understanding route concepts that it's hard to be successful without a couple of training camps and a lot of reps.
The main ones I can think of are Terrell Owens, Jerry Rice with the Raiders, and Randy Moss (the Patriot version, not the Oakland version). Moss and Owens were physical freaks who didn't have to run precise routes to get open. Rice was probably the G.O.A.T.
For every one of those there are a lot of Greg Jennings, Mike Wallace, Alvin Harper types out there.