I wear footed tights under leggings for practice, and I have 4 pairs of them that get washed weekly and rotated. I've only been skating seriously (3-5x per week) since July, and I've needed to replace 2 pairs. Tights do seem to have a limited lifespan.
I wear OTB tights for competition, and I have three pairs of those. I buy a new pair after the old ones get a hole in them, which seems to happen after about three events. So two of those pairs have holes, and I doubt I'll wear them again, but they are in too good of shape to throw away otherwise!
Thankfully I scored those for half off at a dance store clearing out their skating section, plus I had a living social deal, so they didn't cost nearly the normal $20 per pair!