Reducing the amount of work the alternator has to do is definitely a good thing. My alternator has been mostly "out to lunch" since Feb. 28, with very nice results, thank you. Please see my project thread:
http://ecomodder.com/forum/showthrea...tml#post286282. You can also see my gas log, see my info at left or my signature's graphic.
Charging at more than "correct" voltage definitely isn't good for a battery. Boiling the acid bath is the result, which means the acid will vent so you will lose some of it every time it boils.
Short of doing a full alternator delete or "EPES" as I did, I suppose you could substitute a deep cycle battery for your standard "starter" battery. Charge it on a correct charger before driving and your alternator will have somewhat less work to do. But the bigger gains come when you can drive with the alternator's output wire disconnected or switched off. Or better yet, remove the alternator belt. I didn't take that last step because I want to be able to quickly restore the alternator to use.