vintage versus modern speakers

I agree with Mapman to a point.

The JBL L100 Century was and is still one of the best rock-
n-roll speakers ever made, if they're in good shape.

The Infinity Gamma, Beta, Sigma, some of the RS series are
still very good, again, if in good shape. One of the only
speakers I've ever regretted selling out of the hundreds of
speakers I've owned were my Betas. I still kick myself in
the ass every so often to remind me of what a dip shit I was
for selling them.

So it really depends on the speaker model and the condition,
but for the most part, today's speakers are better.

are great vintage speakers (Infiniti, JBL,Sansui, Sony, etc..) from the seventies better sounding than what is available now?

Absolutely not!
And while the Japanese companies built great electronics during the 70's, their speakers were very poor when compared to some of the classic US brands like AR, EPI, KLH, etc. But even these acoustic suspension designs of yesteryear cannot hold a candle to well designed and engineered modern offerings.

No contest vintage a joke now.

My main speakers are B&W N801, up until recently I also had a pair of Yamaha 1000M speakers, 33 years old. Of course I prefer the N801 speakers, but are they worth nearly 10X the price of the Yamaha's? Probably not. The Yamaha speakers have a unique, very revealing sound.

I can still remember hearing a pair of Klipschorn speakers at a HiFi show 35 years ago, they sounded truly amazing, the most dynamic speakers I have ever heard. Similarly, as one poster commented, JBL L100 speakers still sound great on rock music.

So in answer to your question, there are some amazing sounding vintage speakers still available. At the end of the day it is all down to personal preference.