I don't have any information to back it up, but I am of the opinion that Bar-status spells scale in potency with enhancing skill, at least up to the 500 cap given that:
A) Bar-element spells scale in both duration and potency with skill, and
B) equipment exists that lists status resistance with numerical value, suggesting that they might use a similar system for spells and abilities that buff resistance and that value would potentially scale with enhancing skill.

At this point I think that they should just remove the skill cap for all enhancing spells, the two most powerful enhancing spells RDM has access too (enspells and temper) are already uncapped, the others would really only be minor buffs.
Phalanx: we can already buff phalanx with certain equipment, equipment which does not also have any enhancing skill on it, which would mean we would have to balance phalanx+ gear with skill gear, resulting in only a minor increase at best.
Stoneskin: is a joke at this level, even uncapped probably wouldn't be much better.
Barspells: are the only thing that might be significant, since they are already overpowered when stacked with songs and runes, however they could easily uncap only the self target barspells, since WHM gets so many buffs to them that even an uncapped RDM couldn't hope to catch up.