I have a couple of suggestions for making it more rewarding for FvSs and Clerics to heal the party.
1) List the average amount of healing per spell that the caster has done, and the total amount of healing done to the rest of the party, in a given quest. I would suggest listing this information just above or below the kill count.
2) Let there be an enhancement for FvSs and Clerics, call it "What Goes Around, Comes Around". This enhancement would give a 5-10% chance for a regeneration effect to be cast on the caster whenever he or she casts a positive energy spell on the party. Lets say 1d3 positive energy every 2 seconds for 20 seconds per 5 Cleric/FvS levels.
3) Make Haggle a class skill for divines