I did get a pack of bootlegs in the '70s (not knowing they would be at the time) from somewhere down in Surrey I think (Gwen Owens, Porgy and the Monarchs etc), but the Soul Bowl packs were definitely the most interesting.
As I didn't have many records at the time, I was thankfully fairly liberal about what to keep, plus I was happy enough if I just liked it, irrespective of whether it struck me as 'Northern' or not. I must have got rid of quite a few still, but I think I'd typically keep maybe 80 or even 90 from a 100 pack. I enjoyed flicking through and playing a few first ones that I thought I knew, and while doing so, going through the rest checking both sides and deciding a series to next play through.
As you say, tastes change over time and I still find flip sides to the ones I thought were the 'good' ones that catch my interest. Tape swopping was the key for me, needing to dig into what I had to try and keep on top of returning the favour of great tapes of music that dropped through the letterbox!
A bit off topic, but I got some really good general soul 45's from Black Knight back in 1998, stuff like Pat Cooley 'I'm giving it all I got', Shirley Brown 'I don't play that' and Frederick Knight 'When it ain't right with my baby.'