Say what you will about 4th edition D&D (which is now itself on the way out for 5th), it did have a very handy concept that should be adopted in this game: healing surges.

The idea is pretty straightforward: every character has a number of "healing surges" equal to their constitution modifier per rest. These surges can be spent by a character to heal themselves 1/4 of their total hit points.

Now, actual implementation in 4E is a bit more complicated than that (most characters can only spend one surge on themselves per encounter unless they have special class abilities that let them do it more than that, for example), but in DDO I think it should simply be an ability with a relatively long cooldown (1 minute or so) and a number of charges equal to Con modifier + a bonus based on class (basically give extra starting surges to the beefier classes that will most likely need it more). Let healing amp work on it as normal, and include various feats/enhancements/ED abilities/etc. that beef up the ability in some fashion or another.

This wouldn't replace the importance of other sources of healing, but does give a little bit of extra breathing room to fighters and barbarians in particular and eases up a bit of the burden on divine classes.

I'm sure this has been mentioned before, but it seems time to bring it up again. Thoughts?