I've been playing L2 for about 2 weeks now and must say I am very impressed with the game as a whole.
I've tried several different characters and have a question concerning mystic buffs and spirit shots. Do spirit shots do anything at all for buffs? By that I mean, does the buff get anything special if the mystic uses a shot when he casts it? I'm betting the answer is no, but wanted to find out for sure.
I asked the same questions when I started, but I asked rather late. Had been using them all the time, beforehand. What a waste.
Blessed Spiritshots and/or just Spiritshots do not increase buff duration or stats of said buffs. All they do is decrease the casting time of the buff and the casting time between buffs. Meaning you cast buffs faster and can cast the next buff faster (recharge of same buff).
When you are say planning to nuke or heal, these do provide more damage dealt and allow you to heal for more.
Healing variation differed depending on level. 1 - 20 heals increas like 50 HP, 20 - 40 give nearly 100 more, and 40+ gives like 150+.
E.G. my EE is 54 with Greater Heal 6, heals for like 475 normally, pop a bsps on it and heals for about 635.
I think it is somewhere around the same effect as for nukes. I think the amount is higher than you describe it, and it's not raised by a fixed amount. Power of heal is also very slightly affected by matk, but it's nothing to make you crave for top A. Difference between NG and A weapon for me is like 60 HP.