/Shop should be left in place to keep a level on the economy. Without some form of solid base, the server's economy could collapse if a large enough group of players got together to inflate or bottom out something. (granted, I'm sure an admin or Mod would take steps to prevent that from happening)
I think the buy prices on the /shop are good. a hefty margin above what an item is really worth. Some of the /sell options could be modified a bit. Adding redstone as a cash commodity would be wonderful for inventory space, but the price of selling it would have to be ridiculously low. Perhaps 2nbz/5redstone or something of that nature. I agree that not all things should be added to the /shop buy or sell though, as it will keep that incentive for players to frequent market district more. So my vote on the poll should be split 50/50