Agree that Wet 'n Wild is just fine. El Paso certainly could have a better amusement park, but Western Playland has had no competition since Magic Landing so they've become complacent. (Although they did add a roller coaster in the last decade, but it's nothing special from what I can tell.)
El Paso won't have a Six Flags in the foreseeable future, but for what El Paso
could and
should be able to support, look at Adventureland in Iowa, close to Des Moines. El Paso has, what, about 700,000 people? Des Moines has about 200,000? (The Des Moines metro, including Ames where Iowa State is, approaches the population of the city of El Paso, but then the El Paso metro is bigger than the Des Moines metro.) And people from Juarez WOULD visit El Paso for a quality amusement park, so add that to the El Paso area population. Adventureland has 5 roller coasters, two of which have inversions and two of which are classic wooden coasters, of which Western Playland has neither. I mean, if the middle of freakin' Iowa can support a quality mid-level amusement park, there's absolutely no reason El Paso can't. But Western Playland has no incentive to improve because El Pasoans are complacent (they'll go to Western Playland because it's the only game in town) and there's no competition prodding Western Playland to improve.
As for another suggestion, I've floated this idea before and I'll do it again. One thing El Paso has over the rest of the state is that we have mountains. San Antonio and DFW might have Six Flags, but we can build something that they can't: a mountain (or alpine) coaster. I've ridden alpine coasters in the Smoky Mountains and they're fun. We could build a mountain coaster on the side of the mountain with a great view of the city on the ride down. It would be great and unique for El Paso, the only ride of its kind in the state of Texas.