I don't need five 35mm cameras...but it has helped having five or more on many occasions. Redundancy can be key if you are seriously using your equipment day in and day out in various situations, which I probably do at least twice a year when traveling by road. It sounds crazy, but having six 35mm SLR cameras with me on a trip comes quite in handy. I shoot three main ones (two old F-1s and a Nikon F), with 28, 50, and 135 lenses, all loaded with the same film.I keep these out of the case and within easy reach. However, I also keep a low-light body/lens combo (55mm f/1.2 loaded with Delta 3200), and a long telephoto body/lens (200mm f/2.8) loaded and in the case. I also keep a loaded AE-1P backup body in the case to quickly take the lens from a broken body without much wasted time. AE-1Ps weigh nothing, cost nothing, and can save the day if the situation arises (which it has, for me). In the situation I was in, my subjects were changing constantly, and so was the way I was shooting. I almost always find myself needing at the least an additional dedicated low light body, as my standard film is 400, but I use 3200 for low light. Fooling around with unloading film halfway through a roll is not something I want to do every time night time rolls around. I find it highly helpful to not have to change lenses all the damned time. Personally, I find having multiple camera bodies 100 times preferable to swapping lenses all the time.
I am pretty much set with two handfuls or so of 35mm cameras, and I do think that having any more might be far less important than film. However, I do think that I prefer to work with an extensive kit that is ready to use quickly and easily, and which will allow me to easily handle the loss of equipment due to its failure. Two of the great benefits of 35mm are the size and cost of the equipment. All of that equipment I mentioned fit into one case, with the exception of a loose Nikon F. Additionally, adding it up in my head, all together, the equipment cost me under $800, so it is super easy to justify the gluttony in that respect.
The only 35mm SLRs I have that I don't really use are my Spotmatic, my K1000, and my EOS 3. I got them just because they were dirt cheap. I got the Spotmatic and K1000 for $5 each (with lenses!) just to serve as a base for any interesting and cheap M42 or K mount lenses that might come my way. I got the EOS 3 for sharing lenses with digital equipment, since I have one really nice EOS lens. However, I find myself using it as rarely as I use digital, even though it is an outstanding camera.