I know the balance issues and troubles that have gone into this tradeskill before I even suggest this. I also feel it needs a new overhaul in the future, but I am not going into that. I am suggesting a current balance issue that IMO has been needed for some time.
With that aside, I think that infusing needs to have a 5th level druid spell gem/wand and 5th level cleric spell gem/wand to go in line with the current Firebrand spell gem/wand.
I suggest for the cleric to put in either Circle of Doom or flamestrike. Neither of these spells will be over powering in a wand, it will simply give a cleric the ability to level up their infusing on par with a sorceror and wizard.
For the Druid spell I suggest inferno. Again this will allow a druid and cleric the same leveling abilities/advantages that a sorceror and wizard currently have. After all there are staves that only a druid/ranger can make due to the requirment for the spell camoflague memed to make the staff.