I have just slightly shifted but not wholly different opinions from the majority I've seen expressed on a few points:
Bags as "investments": While I agree that you can't and shouldn't look at a bag as a traditional investment like stocks, bonds, real estate, a thriving busienss, etc. (does anyone really do that?) I DO think it's smart to take a look at a handbag's value proposition. I tend to buy brands that will hold their value. And when buying, I want to keep costs low so use per wear is (relatively) low and I can better recoup my funds when selling the bag. All things being equal, if I'm spending $2000 on a bag (on sale or preowned), can wear it multiple times for 3 years and get $1500 out of it when I sell it. Hurray! That's more $ towards the next bag. 😀 If I only get $600 out of it, I'm not as happy. So for these reasons, I absolutely look at the value proposition of my handbags when purchasing.
Fashion v. style: I absolutely agree that fashion is about trends and external opinion while style is about your personal brand / image you embody by your choices, looks, carriage, etc. And I agree having stunning style is the goal. Chasing trends keeps you on a hamster wheel and limits your ability to develop your own signature.
BUT, I would also say that unless someone is skilled in and devoted solely to a "classic" understated look, that fashion trends can and should be the accent that keeps a person's style fresh. Sprinkling a bit of fun, tasteful new trends into your signature style can often be the difference between looking dated / boring and fresh / interesting. So let's not throw out the baby with the bath water. Many people think they are classic and they are just dated. Some think they are fashionable and they are simply trendy. It's not that either fashion or personal style is always good or bad or that either one should be a state of isolation.
Bags should make us giddy with joy: There is a lot to be said for what makes YOU happy. Unless you work in the fashion industry where your clothes are your "work", indulge your bag passion wherever it leads. If you like an obviously "dated" bag, wear it. If someone doesn't like it, they may not be the right person to hang around.
So, with all that said, I absolutely consider the cost / value / resale of a bag. And, while I absolutely have a signature style, I love reinterpreting that over the years including dabbling in some trends. But, bottom line, if I love the bag AND I'll get a lot of use out of it, I will buy it and happily take any future money or fashion hit.