Hi Dave,
Your first point is good, and one I agree with, as that type of knowledge has indeed dwindled, probably for the reasons you state. However, at least up here, there are still quite a few independent record shops, primarily owned by music lovers, who are able to advise on such matters and who just love talking about music!
They also tend to have a small system set up in the shop, with a turntable, which they'll gladly use to play you records, prior to purchase, especially if like me you enjoy expanding your musical horizons and checking out new stuff that looks intriguing... It's not always just about buying what you know. One such shop near me, is Grey N Pink, in Chester:
http://greynpinkrecords.com/
They've got a Rega P3, set up in a rather nice little system, and the guys are very knowledgeable and helpful, and coupled with the fact that the shop carries a huge and diverse range of music on CD and vinyl (new and 2nd hand), makes it a great place to go. Moonlight Records, in Wrexham, is another such place:
https://www.google.com/maps/uv?hl=en...oiowE3oECAYQBg
I could go on, lol... You'd imagine that there must be many places like that in London, if you know where to look!
Marco.