Polk vintage speakers, great quality at cheap prices

I'm sure others here will chime in soon, but I would have already bought those. They look to be in excellent condition and you could easily flip them if you didn't like them.

They look good, and a good price, even "if" a driver was frozen. If I were within driving distance, they would come home with me.

Even if it had a frozen driver, you're stealing them for $150! Go grab them. There are plenty of people here with spare drivers or, I'm pretty sure you can call up Polk Audio customer service and get replacement/upgrade drivers. Totally worth it and honestly, out of the few Monitor series speakers I've heard these are probably my favorite and they have a cool factor with the exposed crossovers.

As far as your questions on JBL, the ones you reference are studio monitors. They weren't necessarily top of the line back then but they were a nice speaker for a nice price. However, finding them in good condition is rare. Many need to have a re-foam job done on the woofers. So a good pair will get top dollar to a collector. At the same time though, $350 back in 1978 bucks was a small fortune. $350 now is peanuts comparatively. They didn't really hold their value. Because they were in that magic range of $100-$500 back in the '70's, they have maintained a price but the price point has dropped invisibly due to inflation. In other words, they may still be around $300 a pair but $300 don't go as far as it used to. They aren't maintaining value because of interest but rather because they don't hold up well over the years so demand is a bit past serviceable supply which keeps values a bit higher. Not necessarily because "...fan's strong loyalty keep their vintage speakers at higher resale?"

As far as the Polk speakers, the surrounds on the woofers are likely rubber and they won't degrade as much or at the same rate as the foam surrounds on the JBLs. Given that, there are many more still around that are completely serviceable. Most repairs/upgrades are related to crossover components and wiring which are all readily available and fairly inexpensively because of standardization for the entire electronic component market, not just audio. Add to that the fact that Polk Audio still supports it's old models as best as it can and you can see why the speakers have remained attainable and in ready supply. JBL doesn't support much past 6-10 years ago.

Get those Monitors and if you don't have amplification, get a NAD amplifier to power them. A 902 would be easy to find, fairly cheap and more than adequate to get decent sound out of it and you'll love those Monitors!