I've learned that the simpler and more nondescript the style, material, and pattern (actually lack of pattern), the longer an item stays "in style." So they're my core, basic bags and I spend more money on them. Of course, Plain Jane bags aren't as exciting as the latest "it" bags so I purchase less expensive, trendier bags for fun.
I learned yrs ago that there is no such thing as "timeless" style. Everything looks dated eventually. Just look at family photos or yearbooks - yikes.
However, styles come and go.
And come back again.
Think Birkenstocks, Grace Kelly frame bags, 1960s hippy --> 2017 bohemian look . . . My great niece is begging for my original Dr. Scholls, another niece discovered my trunk of 1970s Disco Danskins outfits but also fell in love with my 1960s hippy deerskin crossbody with fringe.
I suggest buying what makes your heart sing. When it goes out of style, and it will, either continue to wear it bc you love it and don't care what the newest fashion Gods decree, or, save it until it comes back in style. And it will.
JMHO.