One of the things that makes many build options non-viable, is that they reduce your caster level too far, or in the case of bards, your song level.
This means that you are either encouraged to take as few class dips as possible as a caster and/or bard, or to take levels in Evangelist (for bards only, a cheesy thing that is OP and likely to be adjusted). Loremaster is commonly taken as it STILL boosts caster level and song level, even if not by a full amount.
It also means that mundanes do not want Archmages to cast buffs on them, because that will make them easier to dispel than if they drink a potion, which makes absolutely no sense.
Suggestion: Add a Practiced Spellcaster/Singer Feat
This feat would add +4 caster level and/or song level to the character, but can only be taken once.
Doing this would allow for more build diversity, but not hugely so, at the same time as coming at a cost (feats are usually quite tight on casters and on bards).