Currently, in PvE caster shamans, resto shamans and holy paladins are super far behind every other competitor.

Instead of a revamp to the classes themselves and their scaling an option could be to buff the amount of spell power provided by all spell power shields in the game as they are the only people who are able to use the item. It may add some diversity to content past t5.5 in terms of dps/healers.

Thanks,
Samlol