Other than the BBWAA, it's difficult to find an outside source of a significant size of people who should have a high knowledge of baseball that has reasonable turnover with time. Outside source being key. The fault of letting the players choose has already been noted. I'm not so sure front office employees are the way either. They would probably find a way to develop a computer model that maximizes arbitration outcomes in their favour based on who they vote for.
It might not be too popular of an opinion, but in general I think the BBWAA has done a decent job in choosing players for as long as I can remember. It's only since the steroid issue has voting come off the rails. And things like social media being used by the voters to gain attention and stroke their egos. But would either of those things end up differently if another group voted?
Outside of the players immersed in the steroid scandal, the biggest controversies have been Walker, Raines and Blyleven, all of them correctly voted in at the last moment according to the consensus of the "smart" stat nerds. Morris who was correctly left off. Schilling and Vizquel where based on vote totals now it's looking pretty good for the former and not too good for the latter. And then some random writer gives a pity vote to someone like Adam Dunn knowing full well he's not going to get in which gets some people's panties in a knot.
But as a strict yes/no narrative, I think it's been fine. My biggest complaint was Lofton falling off immediately but he probably doesn't get in anyways if he is considered just a shade lower than Raines.