Unlimited Heal (~90 HP) wouldn't be overkill, especially with a cast time of 8-10 or something. Hell, even GHeal with a cast time of 15 or so wouldn't be overkill. But this is an old world item and I highly doubt that the old world zones will ever be looked at and revamped to bring them in line with the new worlds, so this will always be a crappy 1 charge SHeal. Does anyone EVER use charges on non-throw away items?!? I know I don't.
If it had some insane number of Gr Heal charges, the area would become overcamped (like AC). Could you imagine the effect of an endless supply of Gr heals? My God, the cleric would never go OOM. (At least not until he tries to heal 45+ tanks with a little 300hp heal *heehee*)
IMHO, it's like soufire's Complete heal charges, they are there to save your butt someday; but the item's stats are the reason you carry it.