The paper will last quite a while as long as your sanding off too much CA glues with it. I changed mine only 3 times last year and I did quite a bit of sanding. You can always give it a brushing to get the grit out of the pores, but I never bothered.
The glue will not bother you until about the third changing.
The excessive leftover glue can be cleaned off with some acetone or lacquer thinner. Sometimes I even take another piece of sandpaper and use that as well to clean off the sanding bar.
Don't forget to buy a spare rolls of paper, comes in 4 grits that I know of. I use 150 and 220 grit.
Or if you buy the GPMR6169 model, it comes with one sheet each of 3 grits. 80, 150, and 220.
http://greatplanes.com/accys/gpmr6169.html