I would say it depends on how good the price is. If it's at or more than half off the price of the new style, it's a hard value to beat.
If this 90's plossl is a smoothie, here's a couple things you'll be missing out on when compared to the modern day version. One thing is the rubber eyeguard which you may find helpful to block stray light if you observe in less than completely dark surroundings. Another is the ability to use the Tele Vue eyeguard extender, which can help for those that find the eye relief a little too generous. This also applies to Dioptrx compatibility if you wear glasses for astigmatism. And of course, as you mentioned, the upgraded coatings due to coating technology advancements. I'm sure on a bench it would read as having a higher throughput, but if that's detectable by your eye I'm not sure. I would think the differences in light throughput when comparing two eyepieces of the same design but with different coatings would be more noticable as the number of elements and air to glass surfaces go up.
On the other hand, vintage Tele Vues don't have undercuts