I just tested this level 42 spell Boon of the Clear Mind (Boon) against the level 14 Breeze and level 26 Clarity (c1) on my level 43 Enchanter today.
Looking at Combat Mana Regen (cmr) in the character stats screen in game I see the following:
Breeze: 7 cmr
c1: 10 cmr
Boon: 7 cmr
I made sure to remove each spell from my buff window before casting the next to confirm the change in the stats screen.
I assume that Boon will scale up to 10 cmr with character levels nearing 65 to match c1's 10 cmr whereas Breeze is capped at 7 cmr but I am completely ignorant as to how spell scaling works in Everquest.
I feel inclined to mention that I am playing on the time locked progression server Agnarr although I don't imagine this will have any influence on how the spells function.
Personal thoughts:
I was very excited to finally gain access to a group wide mana regen buff but that excitement slowly faded away when I noticed that Boon failed to override a lingering c1 buff on one of my party members. I'm just a bit disappointed that boon, at my current level, is inferior to the single target c1. I do appreciate the convenience of applying some mana regen to my entire group in one single cast but I can't help but feel that I'm letting my group down, ever so slightly, if I choose this spell over c1. In just a dozen or so more levels the difference in these spells will be largely irrelevant to me but I can't help complaining.
I hope somebody will find this helpfull. Cheers!