I agree. I think that most people who have a large selection of soaps has a rotation of different soaps that they use, so even if after a couple years some of their soaps lose their scent, its not a huge deal.I used to think the same way and since a puck of something like Tabac would last me more than two years, any stocking up was out of the question.
I finally realized that the people with large soap collections aren't buying the soaps with the thought of using them up. Spoilage is really not rellivent as they have more soap than they could use anyway. They just want to own and try different soaps. So, with that thought in mind, too many would be when your collection starts negatively affecting your life.
I still have a very modest stock of soaps, one and a half Arco sticks and a hand full of samples.
Personally, Im someone who uses 1 soap until its gone and then picks another, so for me, theres really no point in having 20 or 30 soaps on hand at a time.