Nice family photo there, OP.
I am in similar shoes, minus all your cameras except the XTi! I plan to order the 6D when it's out, if not even preorder one. I have considered selling my XTi, 2 EF-S lenses, and my Sigma 30, all of which would fund maybe one good L lens for the 6D.
I have 2 old EF lenses from my film days, a 20-35 f/3.5-4.5 (a good lens, not the best, but good), and the EF 28-80 kit lens (pretty much a piece of crap, but it takes pics better than no lens at all).
I've kept all that kit (Film Rebel and old EF lenses) on display in my office next to some other cool camera stuff for 6 years since I got my XTi and EF-S lenses. I love having it on display. And now, 6 years later, I am contemplating using the old stuff again, a thought that never even occurred to me before.
So my conundrum is whether one L lens is worth letting go of my whole APS-C kit, or do I hold off, keep the kit for my display, as a backup, and maybe even pass on to my son or daughter for their first DSLR when they are ready. If I hold off, I would be using the 20-35 and 28-80 with the 6D, and borrowing an L lens from my buddy who has kindly offered until I would have the budget for my own L lens, likely within a few months after 6D purchase.
To be honest, I don't want to let go of my kit. Just can't bring myself to see the XTi, or my 10-22, 17-85, or Sigma 30, go anywhere.