I own a few, but since I bought a couple of designers bags I use them less. Unfortunately one does get used to better quality, but there are still plenty of cute bags reasonably priced.
Now I am more selective and I buy only after I checked many different brands, but if it is for something I know I won't use a lot (like a yellow summer bag) I gladly go for something less pricey. If it is for a bag in a neutral color which I am likely to use a lot, I would go for more expensive.
However, I am not quite sure if you can actually buy a bag "for a lifetime". Firts of all because even the best leather does age, and not well. Even the best quality tends to crack, even if you clean it and "nourish" it with special products. Then styles change. My mother has some cute bags which I won't ever use because they are typical of the 60's (too small, the frame too rigid, etc..) and won't go with my clothes. Finally, I do get bored with using the same stuff year after year. I reach the point I just don't want to see it anymore... or, if I really love it, I destroy it because I keep on using it.
So "bag for a lifetime" is definitely not for me.