The key thing about whether or not these reptiles are "social" is: outside of breeding, are they voluntarily seeking social interactions?
In this thread, we've seen numerous examples of large numbers (and occasionally different species) together, but is that really being "social"?
Look at it this way: I stand in line to see the next James Bond movie with hundreds of other people on the opening night. Do I really want to be crowded near all these strangers? Not really. It just happens that all of us want the same thing and it requires us all to be in the same general location to get it.
I know that analogy is comparing me (a hominid) to a reptile, btu I honestly don't think its that much of a stretch, given the issue. All those marine iguanas are piled upon each other on that rock face because it happens to be a prime basking spot. That turtle is resting on that gator's head because it thinks its just another log, and that gator just happens to be not hungry or not irritable.
True, someone brought up the cases of Nile crocs and Komodo dragons working together to bring down large prey. But again, if you really look closely, these are still cases where all the said animals want the same goal and happen to be in the same area at that time. They are not deliberately seeking out the company of conspecifics to organize an attack.