We ended up going to Corpus after all. We sandwiched it in between some unexpected events. Early May is really pushing it heat and humidity wise, but it was okay this year because a cold front had moved through right before we got there. Word is that on around May 2 or so, everybody there was wearing every stitch of clothes they had--nobody thought to bring warm stuff. We kind of rode the end of that cold front, with cooler than normal temperatures and vastly lower than normal humidity.
But things worked their way back to normal, and when we left last Friday, there were only 3 RVs left, and they were all combination windsurfers/fishermen and they were all going to leave after the weekend.
We did have a huge (unsailable) storm blow in on Thursday. May is getting into tornado season so you have to be mindful.
Here's a photo of one of the more quiescent afternoons:

All RVs have to park in these perpendicular spaces now--our favored sites along the water farther down are now day-use only. Notice the curb stop to the right of the RV, which shows the center of the space next to ours, and to the right of that you can see the corner of the tarp that was used by the space next to that one. That illustrates just how narrow the sites are.
We really lucked out by being in a group of people who didn't use generators, so it was a nice stay. Although all sites had been filled just a couple of weeks before, it was only about half full when we got there. Pretty typical for that time of year.
Unfortunately, there was a jellyfish invasion all spring. The smart people wore full wetsuits; lycra wasn't always thick enough to prevent stings, and all exposed skin (like ankles) was at risk. That was pretty unpleasant, plus they're gross looking.
Still, I sailed every day. Some were in my favored 18-23 range, and others were marginal, in which case I played around with clew-first sailing and very low wind waterstarts. I got blown off the water two or three times, partly because I won't sail anything smaller than a 5.5--other people welcomed the wind. All in all, not a bad stay at all.
We didn't end up sailing at Elephant Butte in New Mexico. We did go look at Caballo Lake, the one just south of Elephant Butte. We checked it out on a weekend (rode bikes over there) and it had boat traffic, but it's probably okay on weekdays. There is a campground in the state park, but there is also a section where you can boondock along the water and it looks like you could launch from there, depending on the wind direction.
Jeremy, did you make it to Elephant Butte? If so, I hope you'd done something to shake the Key West out of your sailing because I think it's pretty brutal out there. I think my strategy is to just become a flat water "specialist."