There might seem to not be a lot in the market right now, partially to the fact that everyone is either saving it up, for some awesome (maybe horribly looking castle), or they are using it on their plots or towns.
Granted some Glowstone might be more difficult to get too (the clusters in the middle of a sea of lava), but that is part of the fun in getting it. But generally, it is pretty easy to acquire a good number of blocks, ( I think personally, while looking for Quartz I have managed to collect 35 blocks, and that was with little effort).
The only items that should be added to the server shop, are either extremely rare vanity items (like @CluelessKlutz's Head), or items that you can't get through normal means in game (i.e. Mob, village, animal eggs, or specially created tools (Glass Pick)).