What cracks me up about these questions is that we do the same kind of things. BF is on his forums at night (s2ki.com and av123.com) where he talks about spending a lot of money on car stuff or stereo equipment. He even gets "Residential Systems Monthly" - a magazine about luxury home theater systems. He spends upwards of $2500 every couple of months on new cables, speakers, etc. but thinks buying a bag is ridiculous for that much money. I complain when he *****es about bills being too high and then spends $900 to sound proof the inside of his car (the car that he drives a few days a month).
Its always the same argument - we say they are stylish, classic, high quality, etc. He says that the sound quality or whatever is better.
It took sitting down to explain the differences in materials and crafting for him to really understand the value of a luxury bag, especially if its a classic you can carry for years. I demonstrated this by opening his stepmothers closet and showing him her rack of Chanel suits passed down from her Grandmother. He explained to me some of his stereo and car stuff in a way I could understand, he even unhooked things and demonstrated the quality of watching my favorite movies.
It never matters who makes the money, especially in a one income household where it all technically becomes "our money". If a stay at home wife popped on here complaining about how her DH blows wads of cash on his boy-toys instead of saving then everyone would get behind her - we support what we understand.
I would suggest finding a relevant correlation to something he DOES like to spend a larger amount on and show him how his reasoning is similar to yours.
Also if you own any REALLY high end bags, you can have them insured and that technically makes them part of your portfolio - my friend is a financial planner and BF has a cousin in luxury item insurance who let me know this.