Of course if they have a convertible that needs to be returned to Nevada, I may be convinced to help them out.

Won't happen. Both are corporate stores, so it's perfectly fine to have a car with TX plates in NV, NV plates in TX, or anywhere else.

When using the "Reserve This Exact Model" option, are there any chances of upgrades?

I doubt it, since you told them you wanted a specific model. If they have one, theoretically they could offer a paid upgrade, if you're interested. However, if I remember correctly, there were a few times, described in other threads, when the guaranteed model was unavailable, and the customer got a nice free upgrade.

Any ride reports on Camrys out of DFW?

Or anywhere....Anyway, the Camry was just redesigned. I once drove the "old" model one-way from Albany, but I heard some things improved.