You're smart for thinking about this issue before you have kids! If it's any help, I have two girls who both went through the 'princess stage' and who had Barbies...and I played with Barbies myself as a girl. Soooo, these are my thoughts, based on rasing my two girls (now 15 & 20). What worked for me won't necessarily work for everyone, but maybe something below will be useful to others.
Playing with Barbie won't make girls airheads or self-absorbed. Parents do that. They do that when they let their daughters grow up buying into the idea that somebody's name on something makes it better than the exact same thing without a label. Or when they give their kids, girls or boys, whatever they want, whenever they want. Kids need to hear the word 'no' sometimes! And they need to learn the value of a dollar!!
JMO, but it's better to give your kids an allowance, IF you can afford it, and when they want a big ticket item, tell them they have to save up their allowance until they can pay for all or part of it. If you can't afford to give your kids an allowance, just tell them when they ask for a big ticket item that needs like rent or food or clothes have to come first. When I took mine grocery shopping, I let them compare prices and we talked about what things cost, or when it's better to spend extra for good quality, stuff like that. Same thing for clothes shopping. Each one was absolutely mortified the first time I took her to a thrift store for 'grubby' clothes -- till they saw good quality items for only a few dollars, often with designer labels on them. Don't get me wrong, they'd rather spend money on new clothes (who wouldn't?), but they know when something is worth spending on and when it's not.
Don't make a child feel guilty for wanting something, it may be REALLY important in their minds. When my youngest wanted an $80 DOLL, I tried to steer her away from it. I told her it cost a lot more than we were comfortable spending on one doll. I figured she'd get over it. She didn't. In that case, I waited until Christmas, and used money we budgeted for gifts to get it for her. (My husband still about had a stroke at the price, lol.) You know what? Seeing her 8 year old face when she got the doll after so many months of waiting was worth every penny. And because she hadn't had her 'baby' handed to her the first time she asked for it, that made it special. She played with her constantly, but took good care of her. She's fifteen now and that doll still sits on her bed.
I was a lot harder on my Barbies, lol, but I used them for role playing, which is a part of child development. They were considered demeaning to women in my childhood because of their deformed body shape, but I never expected to grow up with an enormous bosom and weird painted on eyes. My Barbies ran their own businesses or were international spies, or saved lives with their nursing skill. I guess my mother's refusal to buy a Ken doll make my Barbies more independent, lol! Actually she was shocked when I once explained that my Barbie ran her own corporation with a different male secretary for each day of the week!!
Role playing & adventures got passed on to my daughters as well. I once opened our freezer to find a few evening-dress clad Barbies laying inside. When asked, my 5 year old daughter and her friend explained that they were on an Antarctic expedition.
As far as the princess thing goes, when mine were in the throes of princess-mania, it didn't bother me too much. I just pointed out that if they were princesses, that made me the Queen, so I outranked them. They didn't get to rule the roost so to speak When we read them stories about the Disney princesses, we focused on positive qualities like intelligence, compassion or courage, rather than being special for looking pretty.