We've done a couple of restrings on a couple of our blinds but not "every two years." These things are doing great and they just need to be checked for proper function and then they'll last and last. My wife who did the re-stringing says, "it's not hard by any means, you just have to follow the directions to the tee" on the re-string kit and once you do one, it's pretty easy as long as you keep following the directions. I would say, try it once and see how it goes. If anything, it buys you time.
We're also thinking about eventually replacing these with roller shades but we'd want the dual shades that give you both light and dark shades. Pricey and they would have to be custom so we're not ready to pull the trigger yet. We'd have 11 we'd need to do...all custom sizes. If I could go power, I'd do that as well.