I don't know how easy or hard it would be to incorporate some of these, but here are my ideas. Item spawning isn't allowed, even though the server isn't set to peaceful. Seems like it sort of defeats the purpose of not allowing item spawns. Perhaps you should allow spawning for basic items such as Sand, dirt, and torches.

Maybe you could allow kits to granted, some idea for kits could be:
-Minecart kit: If you want to build a minecraft system, this kit gives Minecarts, track, a furnace cart, storage cart.
-Tool kit: Shovels, pick axes, torches, and cobblestone
-Advanced tool kit: All of the same with iron tools and longer time in between spawns of this kit.
-Farming kit: Saplings, reeds, water bucket, hoe, dirt.
-Combat kit(only if server allows zombies): Sword, bow and arrows, iron armor.
-Privileged kit: For those special enough not to be server moderators, but still recognized significant. Diamond(or gold) tools, diamond(or gold) blocks, diamond(or gold) armor.
-Decorative kit: Wool blocks, dye blocks.
-Electrical kit: Redstone wire, redstone torches, buttons, pressure plates, switches.

Also, perhaps a system could be implement to request items for special projects. For example, one could state they wanted to build a spleef arena and would request lava buckets, wool, dyes, glass, and obsidian.



EDIT: Retudndro had the great idea of getting the mod that allows one to lock chests