I am one of those that does mess around with them, cleaning and dry-burning as needed, yada yada. I only recently threw out two of my clearos that had been syringe modded (actually binned a third one today). They were a couple of months old (the third one maybe a month old) and probably started dropping off in performance a week or two prior to that.
Basically, how long they last you will depend on how much of a drop off in performance you're willing to deal with and how much fiddling you are willing to do
Heck, at the price of them, even if you only get a week or two of prime vaping out of each one you've gotten your money's worth from it