i actually use sanding sponges/blocks. i use the medium and fine grains (the sponges are 1 on each side): medium to round off big chunks and fine to smooth.
i've put huge gashes in discs (including champ/z plastic discs) and have used sanding to smooth them off.
the main draw of champ/z plastic is that it doesn't warp.
the lifespan of discs is dependent upon how much you throw them and how much you hit things. i rarely throw any one driver more than 3-4 teeshots per round of 18 holes and dx drivers end up lasting me like a year each before they become so understable that i only have use for them as turnover/roller discs. if i were to throw the same driver on all 18 holes a round, it would drastically shorten its lifespan.
when you look at basic durability there is:
1) how well the disc avoids dings/scuffs
2) how well the disc avoids structural compromises
3) how well the disc can be repaired from 1 and 2
with dx it is easy to smooth and easy to unbend any warping.
with mid grade plastics they are much more scuff resistant and they are slightly more durable when it comes to warping, but they cannot be unwarped once they are done.
with supre premium plastic they avoid 1 and 2 well, but they are the most difficult to repair if 1 and 2 occur.
with gateway you would likely have to buy online. they have very sporadic stock when it comes to their E line, so if you are looking for something easily replaceable i would probably recommend the z xpress and champ leopard ahead of it.
the shop i work at, www.gottagogottathrow.com
has the majorty of the discs offered on the market.