Well, I currently own five sewing machines. I only had one at a time for the first 35 years of sewing. Now that I've expanded to quilting in the last several years, I have formed an appreciation for a variety of machines and am learning their strengths and weaknesses for the type of sewing/quilting that I do.
Like someone else here mentioned, I haven't spent much on my 5 machines because I've shopped for the deals and/or was fortunate enough to have them land in my lap.
I have these machines:
Bernina 730 Record - 60's vintage, mechanical, sews ANYTHING, like a tank. Easy to maintain. Had it since 94.
Bernina 1090- 90's vintage, is electronic and has a variety of stitches. My everyday machine. Has an excellent stitch. Not too much to maintain. Had since 08.
Singer 201k treadle - 50's vintage, recent acquisition, need to learn to treadle. Hear it is good for those of us with MS. Easy to maintain.
Singer 301A slant needle - mechanical 50's vintage, STRONG machine, excellent stitch, easy to maintain. Recent purchase.
Baby Lock Decorator's Choice - purchased new several years ago. Has many, many different stitches, is electronic so can be fussy and is expensive to maintain.
I like to be able to have a couple of machines set up to do different things as some have mentioned here. Some are better at binding, piecing, quilting, etc. The Singer 301A is light enough and portable to take to classes with me. It is the big sister to the Featherweight, much less expensive and a stronger and more capable machine.
I guess as time goes on, and we try different machines and/or hear others speak about them, we have the desire to own a variety of them for ourselves. It's not just about collecting them, as they are all useful in their own ways; I think it's more about appreciating and celebrating their differences and beauty. Each machine becomes an extension of ourselves, our creativity and personality. We all buy different fabrics, don't we? Solids are nice, but when we add prints or novelties, or work with batiks and different colors our creativity soars. :D