I wouldn't retension the wheel unless I had an accurate way to measure tension. I would first check for cracks in the rim around the eyelets, or loose eyelets. After that I would just keep truing it as often as necessary, but I would record EVERY tension adjustment I made, including the amount of adjustment and the exact spoke.
I had once had a wheel that had to be trued almost every day. After a while a spoke broke, and after I replaced that spoke it was perfectly stable for years. If I had paid attention to the adjustments I had been making, I could have identified the problem spoke before it broke, and avoided a long walk home.
OTOH, if those wheels only have 500 miles on them, I'd be looking for warranty help as well. Documenting the adjustments you make will either help your case or void the warranty.
em