So far, testing with stats:
Con has no effect at all on HP gain. Not entirely sure what affects it, but a Sage with 90 Con has 20% of the HP of a Warrior with 40 Con. In fact, the Sage is still liable to gain 2 HP per level even at 90 Con.
Dev has no effect at all on Magic gain. A character with 30 devotion can have the same if not more Magic than a character who has had 95~100 Dev for the past 5 levels. It also has absolutely no effect at all on Magic regen, this is based on Race and Level more than anything it would seem.
Wis has no effect on duration or power of buffs, and healing is entirely based on a die roll. This is between a 56 Wis Bard and a 100 Wis cleric, both had buffs of equal power. If wis does anything for spells, it might make it easier to apply status spells as suggested by another anon, but there is no way to test this as practically, and instruments are better regardless.
Int has no effect on damage of attack spells, this is purely based on dice roll/power level, and fizzles appear to be based completely upon Skill Level. It may effect skill point gain, but I have noted no difference in a 100 Int Sage, who seems to gain 6~20 Skill Points at starting int to 100 int, this appears to be more based on luck when they level than anything and can be savescummed.
Have not yet tested Str or Agi as there isn't too much of a practical way to test them, but Str does increase at the very least, max weight allowed.
DES has a chance of preventing death with a % based on the character's DES. With 80 DES, the character appears to avoid death with at least a 60% chance, while a character with 10 DES appears to avoid death with a 3% chance. This is testing with 100 deaths and is not entirely accurate.
This is testing between characters with 90+ 40 in comparable stats.
