Most often than not, when playing optimally the rage or RP cap won't be reached at all and this talent just seems like a "noob trap" for people who are playing suboptimally to believe that this 5 rage/RP might be a good thing. Normally this passive is going to be completely useless.
With energy comes the problem of 5 energy not being close to as good as 5% mana or X% primary stat (other races). 5 energy doesn't really allow for any new attack to be inputted or for any burst sceneario or new combo. Even 1% agility would probably be better overall than having a 5 energy extra on your cap.
I propose changing Expansive Mind to a resource saving passive instead of raising the maximum for specific stats. Let me illustrate my idea:
Spells and Abilities now cost 5% less mana, energy, rage and/or runic power
I think this makes the passive much easier to understand plus it achieves the main purpose of giving 5% more resources to Gnomes (independent of what resource the Gnome uses). 5% might be a bit too much or too little and the number might have to be tweaked, but the concept is what seems to be good. This is also actually useful for Rage and Runic Power users and allows for easier time actually planning out a rotation or attack pattern as the number on the tooltips would change to reflect this and the player would be able to know exactly how much everything costs.
To better explain why the change is good I will give out an example. With the current passive: a Warrior with max (105) rage who uses 100 rage would be left with 5 extra rage, with my suggestion a warrior with max (100) rage who uses 100 rage would actually use 95 rage and be left with 5 extra rage. No difference here, but... A warrior who isn't reaching the rage cap and is performing his rotation in a way where he uses all of his leftover rage is getting nothing from the passive as it currently stands while with my suggestion he would still be saving 5% of his rage. It would not buff or nerf the passive but it would make it useful in all situations and not just niche "save energy/rage/runic power" phases or "burst" situations.