I try to keep my camera stash at one system I love in each format. Everything else I can not justify and even that is a stretch. Most of my 'regrets' I sold again. The only one big regret I still keep around is my investment in a digital setup. I have not touched it for 18 months, but I am still not quite ready of getting rid of it
My workhorses are my Mamiya RZ and my Toyo 45, so having to finish a full roll of 36 exposures before I can change films does not apply. I usually keep 2 loaded backs for the RZ around, allowing me to change in mid shoot. In the end you have to ask yourself how much is too much. As long as you can afford them, I would say do what feels right for you and if it is one facet of keeping you excited to go out and shoot, I would say go for it. The moment all those beauties start collecting dust in the shelf, it might be time to see if your money is still invested good in gear you don't use.