i only use a 50 Gall per day RO, and ive not changed anything for 18 months, still works fine, infact it my TDS is lower now from the RO then it was when it first began (even after the settleing period)
from my point of view, its a disposable item, when its dead its dead, dont know how much the pre-filters are to change though (i guess i should look into it)