I've been using Rain-X and Rain-X Washer Fluid since it came out...probably better than 20 years ago at this point for the original Rain-X treatment. I have never noticed it damaging the wiper blades (or making them fail any faster) or the washer fluid damaging washer motors. The last truck had 270k miles on it with nothing but Rain-X in the reservoir, and while I went through several sets of blades, they seemed to fail more from the effects of sunlight than anything. There are basically two components of Rain-X: alcohol and wax. Its the alcohol that makes it evaporate so quickly, but I'm not sure if its the same type of alcohol they recommend for cleaning wipers?

I've used Anco (they tend to dry rot pretty quick in my experience), Bosch, even Pepboys spineless versions (Icon knockoffs) among others. I like the Bosch the best, but that $25/blade is hard to swallow for six months of use.

I think its like anything else, the longer the wiper blade sit on the shelf, the more time the plasticizers have to volatilize off, which means a shorter life expectancy on your truck.