I used to think "how many machines does one woman need?" in my effort of downsizing, and simplifying life. Turns out it depends on what projects you are sewing.
Excessiveness is having too many machines collecting dust, packed away somewhere, or otherwise eyecandy. I used to have just 1, then I needed a serger, then I found out the hard way I needed a backup machine for when the '1' was in for repairs, or died. So now I have 4 machines, and the latest one is a 301, which can sew through 8 layers of leather (should I need it to), it's perfect for topquilting.
Bottomline: they don't make 1 machine to do it all, so this is how we collect machines.
Blessings,
MaryAnna