I won't say I'm high levelled but here's what I think.
Going pure SPR might not be the best idea. You will probably need some END in the end, even if you prefer to just play as a supporter. Why? Because in this game, your heal actually acts like a fighter's "taunt" if the person your healing cannot taunt it. @___@"
For instance, someone is being ganged by a bunch of mobs, and you keep healing them. After about 8-10 heals (I did a little test with a friend with zombies, but I can't say that's the same for all mobs) the mobs will actually come after you if the person doesn't taunt it. Thus, you will need some END to at least survive a bit. There is no point in supporting if you die in 2-3 hits at all. You die, and if you're not with another cleric, you will be spawned back to town, and by the time you come back, your party members would have been owned as well.
I guess you can make up the END with rings and things... but you will need to be wearing high levelled stuff to get much difference, and by then, you would need more END anyway since higher levelled mobs hit harder.
I personally went 25 SPR and rest into END/STR (still haven't decided). 25 SPR is enough for your 5% crit, and gives you enough additional SP. Besides, you also have a passive skill that increases your SP. So I suggest you to add some END, unless you have the money to buy lots of scrolls and stones/pots to keep yourself alive. I'm generally poor myself, so I'm not rich enough to get all the expensive things for extra stats and stuff.
Just my 5 cents. xD
__________________
=)

|