Hey, if someone wants to blow €500 on shoes that's OK with me. We all need a little luxury now and then. But just because the money comes from "your" account doesn't mean it's not affecting your partner's financial position. The fact is, as a couple, you are also a single economic unit. When it comes to buying a house, or paying an existing mortgage, the €500 is still gone.
I think having seperate accounts and the culture of individual owership of money above and beyond immediate needs for bills mitigates against good financial planning for the future - especially if it discourages discussion of significant "individual" purchases such as the €500 shoes or a trek up the Himalayas.
Individual purchases still affect your joint position, your net worth as a couple. So they should still be jointly "approved" if your net worth as a couple is important to you. Why wait to have kids to make big changes to financial arrangements? If you've decided to have kids (and especially if you think one of you might cut down or stop working) it might be a good thing to plan ahead financially and place less emphasis on individual buying power.
Just my opinion. All other things being equal people should do what works for them, of course.