Rule of thumb, if you use it regularly, keep it. If you don't get rid of it and find something you will use regularly! Personally when you're using them to shoot I think anything more than half a dozen cameras is an excessive situation unless you're collecting them for the purpose of collecting them, are a professional who needs to have several bodies ready to go or are talking about several different formats that you need to be able to photograph and can't do unless you have more than a couple of cameras, IE people going from regular format, to medium or large format or from those to digital etc.
Some people collect cameras as if they want to start their own museums. I get that, and I respect that because someone has to, otherwise they'll only be lost to time and no info about them will be readily available. Other people use a lot of cameras professionally, or the different format, but people who have 2 dozen cameras or lenses who supposedly bought them to shoot with, and who really don't end up shooting with more than one or two all the time actually rather perplex me.
To me ultimately that's just hoarding, but for the record I don't think you're in any danger of that. 3 cameras? Heck, I've got more than 3 cameras and I'm not the type to collect them at all! That's nothing compared to some people around here, laugh, and at least you USE them, right?