An investment can be thought of in monetary units, but an investment can also have another signigicance. For example, Rolex watches are investments, and so are diamonds. Your fiance isn't buying you that Tiffany rock hoping to sell it five years down the road for profit. It's an investment because you will be wearing it for the rest of your life, therefore the money put in it in exchange for quality and beauty is a good investment.
I believe many women feel this is the investment when it comes to handbags. I don't necessarily buy them only to put on eBay later. I would rather have one gorgeous purse that I can carry three times a week for five or even ten years, that looks great with many outfits, is top quality, and has a classic style, than a cheaply-made, trendy $30 bag. Will I even carry the latter for more than two months?
The cost-per-wear as well as the satisfaction you get from it is where the true value of a handbag is. And in my opinion that's as good an investment as any.