If the purpose of the tomes was to create role-play with their existence, then they should be given to roleplay-centric players or those most interested in using them if possible, unless randomish distribution was also important. i.e. don't give them to people who like building wealth or groups, because amassing power is important to them.
If the purpose was to create role-play, but that's not happening due to the tomes being hoarded, then their use should be mandatory if you possess a tome (or the tome will be reassigned by it's power or something). If the power is something that would be ridiculous if used often, then don't write that as a power OR cause them to decay with each mandatory use. That would force role play situations often, and put time-tables on super powerful tomes.
If the tomes force the user to use them (In hopefully interesting ways for many people) then they could create role play often instead of stagnating in some powerful figures dungeon, which sounds like the opposite of their intent.