I think it depends on the individual and their style.
Some people are the type that move into a bag and carry it for months, or even years, and in that case they probably don't need more than a few bags.
Others are the type that consider bags as accessories, part of their outfits, and change bags daily, depending on what they are wearing or doing that day. I've read here that some people will change bags twice a day.
I don't think even 50 - 100 bags is too much if they are being used. Of course in a large collection, there will be a wide variety of types of bags with different uses, everyday bags, special occasion bags, totes, swing packs, hippies, clutches, etc. Then there's also the people who like a lot of colorful bags to go with their wardrobe.