One of the greatest limiting factors is the "Concentration" factor of the Bards Primary spell list "Controlling Songs".
I understand the necessity for concentration, and agree with it, but it does make it somewhat less effective in situations where it could and perhaps should be MORE effective than standard mentalism casters because of the additional requirements of the related performance.
For one, it's rare that only one target will actually "hear/see" the performance, but easily overpowered if it become (perhaps more logically) all targets within a radius. The limiting factor should be the Bards ability to hold the attention of it's audience on them NOT the other way round!!! In theory Bards could be any, or all the realms. I personally think mentailsm "fits" because the "Songs" lists (specifically) are "only swaying, influencing and affecting minds"
Perhaps,
1. Make Target, "Audience" and simply modify RR by the number of Targets that the Bard is attempting to affect at the same time. (They could chose just one.. or more than one, but do not have to attempt to affect them all.. i.e. 1 target = +0 2 Targets = -20 etc....
2. Then make "Song" effects transferable within the confines (Radius and duration) of the performance. Thus, whilst the Bard continues to perform (Concentrate) additional or optional "Targets" can be selected and possibly affected (getting the above modified RR as normal, with any unaffected then being immune to that specific performance. (This means once a target "drops or leaves the Bard's influence" the spell now continues and be re-targeted or a target that wasn't originally in "range" can now become affected.
3. I'd like to see the option, for "Inspiring Songs". These work exactly the same way as above, in other words the Bard has to concentrate, and focus to affect a number of targets, but these being "allies", instead of enemies. The list could include spells that provide relief in combat (due to morale, perhaps lessening of wound/bleeding/stun penalties.. NB. Not healing wounds simply reducing the penalties whilst actively engaged in other things.) or just straight out bonuses to Melee Combat/MM
4. Involve the Bard's actual performance skill in the casting procedure... Firstly to determine the performances "Range/Radius" plus also to get spell-casting bonuses (like the sort of optional bonuses that Essense casters can automatically get for "Obvious and loud spell-casting" for casting checks.