As to battle damage not being worth it because no one will notice: don't be ridiculous!
Look at Goku when he fires a Kamehameha: his hair is blown back by the force of the blast. Is that something you really notice while playing? Probably not, but it's in there because it makes the experience more enjoyable.
Battle damage would add to the experience of playing ESF. However.. it would cause lag. That's the part that really convinces me; if having a feature interferes with smooth gameplay, I'm not interested anymore.
Even so, if the coders had a ton of time on their hands (which they don't) I would say, "Just add it as a server-enableable feature with empty folders for people to fill with 'damaged' skins." (God knows there are enough on redsaiyan.net.) Unfortunately, the coders don't have a ton of time on their hands, so this isn't a feature we can blithely ask for in ESF, especially when there's so much else to be done.
Thanks for reading.