Well, I own them both (18-55, 24-70) and I don't think the difference is THAT big. The 17-55 is between the two, but of course that means that the difference is around half... I'd first look into the difference in photographers. Since this doesn't involve outright spending money, that seems like a good first move.
There are other possibilities, although they're not "obvious." For example, the 35/f1.8 AFS DX, the Sigma 50/f1.4 HSM (or Nikkor 50/f1.8 AFS), 28/f1.8 AFS and (gasp) 24/f1.4 AFS or 35/f1.4 AFS. I make these suggestions since you already have the 24-70 in the household, and it may be interesting to try something somewhat different. For that matter, the 24-120/f4 AFS VR is also a top-drawer lens that's also not the 24-70/f2.8. The primes are all a lot smaller and lighter than the 24-70 "Chunky One."
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!