It was really cool that the manager at that one Sonic really seemed to want you there.
Nothing dto do with Fieros, but another group I hang out with picks different places after every performance. One time it was a pizza place nearby; this last time, it was also a pizza place; the time before it was a banquet hall. I have noticed that each place they pick is family-owned. No place was a chain. Each owner was a good, solid person, and the food was great (except this last place). At a few places, the owner personally thanked us for coming. My point is, it may be better not to use chain restaurants. I like the family restaurants, anyway.
There is a place I'd love to get to, called Galleria del Paco, or some such. If each place was a destination, but on an off day, results may be better. Not 8 hours, but I'd probably go further for such a place. It would have to be a day trip, for me. If it put extra load on my wife, I couldn't do it.
We had an evwnt where we parked at a school next door, but ate at the restaurant. That was a DQ. We also did a Waffle House and a Burger King. Chains, but we just descended on them.