Rick Spielman is more than qualified for the job. The question I would have is if he will defer to Dave on any decisions? Just how many times has Spielman been overruled by Dave on deals or draft picks? No one will ever really know unless Rick talks if he goes elsewhere. That would be very unprofessional though, and I doubt Rick would do it.
Rick has stated that he knows exactly what he wants to do with the team if he gets the job.
The one thing that will probably keep him from getting the job is the fan reaction. Fans are expecting a change, and by basically giving Spielman more power over Wanny, it looks on the surface like a cosmetic change. Fans in general don't really think things through though. Fans typically overreact to things that go both ways. Wayne knows this, and I think that hurts Rick's chances.
I guarantee you that most phins fans wouldn't know Randy Mueller from Charlie Brown, but the fact that he's someone different will get the excitement up.