It's a bit of a double edged sword really - If the numbers stay high and the income is enough to cover the server costs (and put a bit of beer and pizza money in the pockets of the guys in charge.) then it would be fine to limit it.
In my experience Lower rate server tend to attract "workers" that don't mind putting in the time and grinding until they get the items they want instead of simply spending the money to buy them.
So if it turns out that only a few people are donating, i would be against limiting the ********s.
Dont forget, if you aren't a donator, the people that do donate are actually paying the bills so you can play for free, so please don't be mean to them. (after all if the donators leave someone will have to convince Sam to pay the bills out of his own pocket - something a server host who spends a huge amount of personal time developing a server really shouldn't have to do.)
So far i havent donated to the server, to be 100% honest I dont know how... (is it actually via the gameshop?) the only thing on there that I would actually want to spend money on is the mounts and the desire to do that is dwindling as i see more of the "cool" mount i like the look off.
if they managed to put a winged dragon on the list of things to ride around on, i'd drop £20 on that almost instantly! (lol i like dragons ;-) ) I mean i had to do it for WoW and i left that game about 43 seconds after spending £85 buying all the patches and crap for it.
OOh something else i would spend money on is a skin which changed my archer to look like samual l jackson from Pulp Fiction - if we could change the bow to be a gun of some kind I would throw another £20 at that as well!
Samuel L Jackson with a big afro riding a dragon, shooting zombies sounds awesome to me! well worth £40.