Hi N8YX,WW7KE and Renton.
There can be no doubt the performance of modern recivers surpass many of the past offerings for the price, excluding say a R-390A in good alignment, Racal RA-17, even the Drake R4's and SW-4A .
The DX-150 was my first comms receiver and I had a lot of fun with it, its quite surprising with a good antenna and prudent use of the RF gain what they were capable of.
Sadly mine was pretty deaf above 20 mhz and was subject to 'birdies" but for the price their was little else that came close.
Judicious use of the RF gain generally controlled overload via a large antenna
The RF gain was actually a capable RF attenuator as it effects both the IF and the RF front end as others have noted, the rig had a genuine product detector for SSB and it works well.
A friend who lived down the road from me had an RME -4350 (amateur band only) but in terms of build and performance compared with the DX-150 it was far superior, great selectivity, no spurious responses, and velvet smooth polished alloy tuning knob.
I was determined to step up and I did with a Racal ex military rig, it was an unusual model and used by the Australian miltary, can't remember the model no however it had 5 very tight selectivity options , an accurate analogue dial and hermatically sealed!
An Icom R-71A purchased in 1982 became one of my favorite rigs of all time, excellent selectivity, great SSB, PBT and super accurate readout.(10Hz) I fitted it out with the AM filter, the FL-44A SSB filter and a DC 13.8 volt kit, this led to obtaining over the years my two favorite listening rigs , an Icom IC-761 and an IC 765, very similar in performance to the R71a with extra's, the sensitivity and sound of these is excellent and if required have very clean for (12 volt) finals.
In regard to listening antennas I have a liking for large loops, i find they can be a couple of DB quieter than a dipole or long wire and provide a good signal as well as being balanced for transmitting.
Most rigs improve with an external speaker and I have several Icom/Yaesu/kenwood Comms speakers however for AM shortwave as others note a less expensive bookshelf speaker can provide a smoother fuller sound.