I personally wouldn't spay a mare unless there was a medical reason for it as well. For me the risks are not worth the outcome of her not cycling, and possibly not being quite as marish. In my opinion, if its mood swings, and the squirting ect., then regumate, or something like it to keep her from cycling, and if its just the thought of having a mare that might be moody and marish while in heat, then don't get a mare. I know of a person who did get their mare spayed, but it was because of an enlarged or diseased ovary or something like that, where the only option was to spay her to save her life. Personally I would talk to your vet about all the options including spaying, and see what he/she thinks is the best thing for you and your horse.