I agree with gyg. I also think that the best way to go about 'pimping'* your sales is by highlighting the content, and possibly grouping appropriately. For example, The five or six issues which featured Irilian (easily one of the best cities ever designed for D&D), grouped, might fetch a higher relative value. Similarly, the Cthulhu scenarios in WD were generally of a very high quality, and there were a few really good
MERP adventures. Issue quality also might lift prices a bit, as with many mags of the era that were read and re-read, getting genuinely Mint or Near-Mint, high quality copies, with no staple-rust or creases and still-glossy covers, can be tough.
Otherwise prices will rise depending upon people filling out holes in their collection. You won't be bidding against me as I have pretty much filled out a full M/NM collection from 1-100 (boast, boast, boast, although of course, although I still need a few in the 16-22 range

) Mostly now I buy old dog-eared copies to cut out articles and put together compilations (how geeky is that!)
*observe my mastery of the new vernacular, recently acquired by watching the telly.