Does it feel rock solid? Does it have any lateral movement at all. I'd have thought that a sheet of paper will not make much difference if the screws are done up tight.
I once fitted a status graphite neck to a Fender P-bass. The neck was designed for a J-bass, as I preferred the profile. To be honest, you could probably drive a bus through the gap, but it was solid, didn't move, and sounded fine. I think the gaps were more of a cosmetic thing!
Having said that, I can't speak for the Warwick approach. Maybe if they had a small gap in a new bass it wouldn't even leave the factory (I might be willing to buy some "seconds" though)