Wow Diki that is one hell of a piece of prose so to speak !!!
Incidentally one of the reasons I have always set great store by the value and merits of this forum in contrast with current day reflections on FAcebook,Instagram etc.etc. where one-liners, or at best one paragraph is about all that you get in any kind of conversation be it on arranger keyboards or whatever....

Down to business though !
Perusing your views a few times it explains a lot why we differ in views here about e.g. my adding a cheap yamaha keyboard to my excellent Ketron SD9. Allow me to elaborate.
In contrast with your career ( I'll be hitting 70 in Christmas Eve) I have hardly ever performed publicly, never played in a band ( though occasional with a band) and as such have always been a one man home band so to speak. Initially way back when I learnt to play chords on the guitar, then came the electric organ and synths in the 1980ties and after that the arranger keyboards starting with the Roland E70. At the turn of the century I turned away from Roland and became rather enthusiastic about Korg and to a lesser degree about ketron.
In between 2002 and 2015 I programmed quite extensively on Korg arranger to a point that many considered me to be a Korg expert which I am not, not really anyway. After the release of the PA3X and PA900 I shied away from Korg because they were not compatible with earlier models , at least not with THE REGISTRATIONS, a matter of prime importance to me....

Now being a home musician allows you time. Time to set up things the way you want to and to delve deep into the heart of the arranger keyboard. Here we must also observe the fact that these arranger up till approx. 2012 missed sophistication as regards Registrations ( or User Programs in Roland terminology)
Most of the factory preset registations were computer created and e.g. all acc. tracks defaulted to a reverb of 64 out of the 128 value. Only over the last 5 to 8 years some of them, in particular Yamaha , have improved the preset registrations or songlists, etc.

YOu only have to ask folks even here on the forum that at one stage or another ordered my JS sofwware for Korg PA50,80,500 KMA and PA800 how much it affected the quality of their instrument.....
In other words Registrations in my way of making music are of prime importance and in constrast with "pick a style, pick a righthand sound and just PLAY "..... I guess that is also due to the fact that apart from having time at my hands and not having to gig to me it is important to arrange and try to render the (cover) song in a different arrangement from the original, or at least in a way that it adds something personal to it... As I mentioned before, what is the point of singing "Pretty Woman " with the perfect and identical accompaniment on my arranger keyboard, just sitting in my music room ? It is a different kettle of fish if you have to perform that song to an audience live, who want to be entertained and who want to be pleased hearing the "original version " or at least its proximity....
As to you having turned into a one keyboard only person ( plus computer VST, etc..etc.) I can only say this. Over the last twenty years I have always been a staunch supporter of owing two arranger keyboards of different brands. Three would be an exaggerations granted but two different brands compliment one another excellently. Incidentally the fun purchase of the PSR373 was only due to the fact that my wife thought it would make for a nice gift when turning 70....
Over the last five years I have also tried and master the piano a little bit which is hard work if you only start out at 65, but I get by. A good example of both my arranging and piano work is my recent rendition of Wonderful Tonight, already posted I think but just in case you missed it:
https://www.youtube.com/watch?v=kCMrtPKBqlk

I am also fortunate in owing three (semi) acoustic guitars, nothing fancy mind you, and as such I can muck about with all of these to create a new coversong. ( If you check your email I will send you a link to my latest compilation CD , covering stuff I did over the last 18 months). If anyone else is interested , just ask......

A final word on the cheap Yamaha PSR373 also bearing in mind what Paul said in one of the comments. It is a great fun keybaord with an incredibly amount of sounds styles and even a load of arpeggios. Battery operated if you want to, extremely lightweight and even sporting the Concert Grand to be found in much more expensive PSR models, it is good fun and as Paul said once you get fed up with it you can always make a child or someone else in his or her initial stages a very happy person with it.

Stay safe and have a good Xmas and New Year's Eve.

John