Why Crazy Prices paid for Pioneer 100 JBL L100 AR1 AR3 AR3A

In the mid-1970s I was in retail at Pacific Stereo (a big chain retailer, with 84 stores, mostly throughout California but also with 10 in Chicago and 8 in Texas).  I sold a ton of the JBL speakers, plenty being the L100.  No doubt, they went loud, even with just a medium powered receiver.  I never liked their sound, it was big and brash.  The AR speakers didn't sell as well as the JBL speakers because they were much more tonally balanced.  At Pacific Stereo we had several sound rooms, all with "switching" for A/B comparisons.  Switching from AR to JBL and you were hit in the face with sound pressure.  Customers loved that and most often opted for the JBL.  However, those who were more patient wanted to listen to a full album on the AR speakers.  Only then would they change over to the JBL and listen to that same album.  In that method of demonstration the AR often times got the sale.  They were much more comfortable to listen to for a period of time.  JBL caused listening fatigue while the AR sounded pleasant.  And yes, as others have mentioned, the Advent speakers sounded great and we sold a lot of them, too.  The best method was stacking them, two pairs, placing the bottom speaker box with the tweeter up and the top speaker box with the tweeter down, essentially having two tweeters in the middle and a 10" woofer up top and on the bottom.  That was probably the best "bang for the buck" that I sold.  Of course, the absolute most speakers that we sold was the house brand, Quadraflex.  The ST-19 was a 12" 3-way speaker for $199 each.  They actually sounded pretty decent, and they had a $20 spiff for the sales person.  What fun days those were.

Bought a pair of AR-3A's in 1973, powered by a 55W/ch Sansui 8 Deluxe receiver & Thorens TD160 w/Shure V15 Type III. My first high-end system.
I loved the sound of the AR's at the time but, in retrospect, perhaps they needed more power (55 watts was a lot of power back then).
It's fun to reminisce about the old equipment, but how does one accurately recall the sound of speakers not heard since 1981....?

I have owned AR-3ax, AR-4x, JBL L100, JBL Decade36 over the years. I still have AR-4x and Decade 36. These speakers have the same sound as their siblings for WAY less money.

The nostalgia craze hits most hobbies after 30- 40 years. Anything that was desirable when people were growing up becomes attractive when they are older and have money. Try buying a vintage 70s muscle car these days! Old crap receivers are going for more money than separate amps and pre-amps of the same era. Garbage turntables are being gobbled up, when true high quality ones remain unknown by the masses. LPs are in demand and prices are crazy. Big brand speakers like you mentioned are the rage -but were not always the better performers of the day. They were what the masses wanted, but most could not buy. People forget that most of the old stereo gear they lusted after in their youth was made cheaply to sell at places like JC Penny’s, Macy’s and at the hi-fi chain stores. Most of the low to mid level big brand stuff was mediocre then, and not worth the asking price today -if it’s my money. But you have seen the prices people get for it, and nostalgia is why. If you have any of that stuff to sell, now is the time. This will all end as new fixations pop-up as the nostalgia timeline moves forward. Don’t sell off your CDs! They will be the rage again soon🤑

I have one pair of AR 3 and one of AR 3a, and have listened to neither yet because they were rescued from a recycling place and I want to rebuild-them-some-day.  The AR 3 (early ones) have two salient features: AlNiCo magnets much heftier than later models, and at least very early ones had cabinets made of a Navy post-war overstock of teak wood or some wood very dense and impervious to the elements. 
As for the JBLs, I recall they were great for disco music but not really suited for classical music - maybe for jazz.  They were great in their days, but if one could show me a JBL Paragon system, now that was the nec plus ultra then, and perhaps even now, with all due foam and crossover rebuilds as mandated by all these dinosaurs. 
Pioneer? I had a QX-949 pseudo-quadrasonic, or tetraphonic (but not quadraphonic, a misplaced, mixed-roots neologism, as marketing mavens lured us to remember the technology). I said "Meh!" and sold it.  I preferred my Kenwood KA8006 and KT8007, very elegant design and I think at least equal performers to the aesthetically boring Pioneer corresponding amp and tuner.  Not to speak of my unequalled Marantz 2275, or better yet my 2270 (two phono inputs awaiting my Empire 498 and B&O 4002), which are awaiting the same fate as my ARs some-day-soon.