Luckily my audio purchase regrets were not super expensive. Marantz Reference series and Acoustic Zen Adagios. They were easy to sell so it worked out in the end.
I had Martin Logan ESL 15A's that did a great job with woofer integration. They measured well after running the built in ARC. With that said, after years of trying many different models I gave up on Martin Logan. The sound became boring and the higher frequencies never did it for my tastes.
My experience with whizzer cones is limited to a few DIY drivers (Tang Band W8-2145, Tang Band W8-1808, SB Acoustics SB20FRPC30-8) and Zu Soul Superfly + Omen. They don't suit my tastes to this point but some enthusiasts like them. I'd like to try the Altec 603's you posted.
I enjoy single driver speakers and use them as mains at least 3 days a week. The objective performance is likely not comparable with a good multi-driver build but I thoroughly enjoy them as hobbyist. EQ helps with some issues.
Make sure the speakers can be replaced if there are cosmetic issues. My walnut F208's started to develop little bubbles in the finish months after taking them home. The distributor helped replace the speakers. It worked out in the end but it took a long time to get a resolve.
This time of year reminds me of when I lived in the East. Trips to the White Mountains of New Hampshire, Adirondacks in New York, Green Mountains in Vermont.
I can't recall but I start at 6-7 feet apart when bring in new speakers. They were only spaced this far so I could access the back of my gear. The f208's also have a low frequency compensation switch in the rear.
Years ago I was using Revel F208's with Exposure 3010S2 mono amps. The space was approximately 14 x 18, no attention to room acoustics at the time and a glass coffee table likely causing havoc. The f208's did not cause any major issues in room. I was using a Revel Performa 3 B110 subwoofer as...
I had the Audiovector R1 Arete and Mark & Daniel Maximus Diamond+. The M & D were wonderful little speakers, preferred them over the R1's other than finish. Tiny (see pic) but impressive sound.