Moses Malone, Lafayette Lever, Drazen, Petrovic, Jermaine O'Neal, Jarrett Jack, Aaron McKie, Patty Mills, Jerryd Bayless, Omar Asik, Josh McRoberts, Sergio Rodriguez and Martell Webster.
You're really going to back to a player that were traded 38 years ago?
So, to be realistic, let's go with those in the last 10 years, because going back to 38, 30, 24 and 14 years ago is a tad bit of a stretch.
Those who were Blazers, and you listed:
Bayless, hasn't done much.
Josh McRoberts hasn't done shit in the league.
Sergio didn't do shit in the league.
Martell Webster hasn't improved at all in the time he's been in the league.
Jarrett Jack hasn't stuck with any team.
Omar never played for Portland, so are we going to bring up players who never actually played in a Blazers uniform now? (I believe Moses actually did play in a Blazers uniform for a pre-season game).
You could make a list of this kind of stuff with EVERY team in the league. If this is our list of players that went on to prove the Blazers made a mistake (as you imply), then I'll take that list over most of the ones in the NBA.