It all really boils down to what you intend to achieve with your photography.
Different camera systems call for different techniques, just as much as different lenses yield different perspectives and drawing characteristics. Same can be said for using a specific film or digital sensor.
Although I have three different lenses, a 28, 35, and 50, I rarely ever take an additional one with me. It's usually just one lens, body, and film.
I occasionally paint, and although I have a wide set of paint-brushes and different format papers/canvasses and paint options, as I am learning, I tend to restrict myself to one size paper, and acrylic paint. Once I am confortable with that, I might venture something different, but if you get good at something why not stick to it?
I worked with a Nat Geo photographer in Brazil for a while and he's good at taking pictures from helicopters, climbing up trees, and carrying beastly telephotos. His photos have a distinctive aesthetic, and he sticks to his kit (and subsequently heavy and huge bags). He used to shoot one type of slide film before he went digital, and now uses a full frame Canon body. His kit also includes wides, as wildlife photography
inevitably takes you close to your subject, and it's his knowledge of both what to use and when that defines his technical skill. He's not a National Geographic photographer for his skill alone though....
Last year I participated in a workshop with Mauricio Lima (Time's Wire photographer of the year, 2010)
http://www.time.com/time/photogallery/0,29307,2039390,00.html
and amongst the discussions, gear came up. His answer, one 5D, a backup, plenty of batteries/cards, a 35mm. Sometimes he'll use a 50. He's been to the middle east on a number of occasions and this is his kit.
HCB, one camera, one lens.
What I have found with this method (restricting yourself to a specific kit for specific reasons) is that eventually you begin to get used to a certain combination and understand how that particular combination "sees", leading to, hopefully, consistency in the images you produce.
That to me, personally, is nirvana.