One idea I got is you could scale abilities to tie into staff speed because fast staff is still best staff. For instance say a spell has 5 periodic ticks of damage over x seconds normally. A blackbolt could do 3 periodic ticks while a darkscepter could do 5 ticks. Or how about duration increases of effects such as eye rot, WoF duration, or confusion blind. Its just an example of course but you get the general idea. Also I think the different types of staves need to be buffed. A spellchanting staff should really really help out in buff duration or sacrifice effectiveness.