Well, the presence of Derek definitely gave it a feel and look unlike just about any other Dream Theater tour, so I get where you are coming from, rumbo.
I don't think JLB has the voice to do a solo spot. Remember Freddie Mercury doing those and the crowd mimicking what he'd sing? Very few rock singers can pull that off well. And DT has never had a secondary backup vocalist strong enough to support such a thing like, like Scotty alluded to. Portnoy and Petrucci are/were both more Steve Howe than anything vocally, and with DT never having a Chris Squire (a very strong backup vocalist, who can be a great number 2 and occasional good number 1), it just would never work. It's too bad that DT never has had a really good number 2 vocalist, because looking at DT's career as a whole, while they've had their moments, great vocal harmonies are one thing really missing a lot of the time.