I'm not sure if this was suggested before. I'm too lazy to search the forum.
Most casters uses Rune of Evasion on their staff as there are no other option. Why don't you make a new rune, the "Skills Cooldown Rune"? It can only be enchanted on Staffs. It will give an enchant value based on the level of the weapon. For example, a level 18 staff will get 1.8% as a common enchant and 2.1% for great charm.
And also, make a "Life Steal Rune" that can be enchanted to cloaks, amulets and shields. Once it's enchanted, it will give an enchant value based on level of equipment +0.5%. For example, a level 20 shield will get a 2.5% as a common enchant value and 2.8% as a great charm value.
Thank you for noticing.