I've always felt totally alone falling somewhere between 
    hardcore audiophiles

To me, the "hardcore" audiophiles are the ones who understand a bit of actual science & engineering and don't go chasing ridiculous crap like audiophile USB cables.

The lunatic fringe gets all the attention, because they're comically delusional, but they are not hardcore to me.

    or whatever audiophiles spend

Bought new, the modern equivalent of that $100 Craigslist system is (vast simplification and approximation) about $500. A well-researched $500-$2500 (new) stereo system is in my experience and opinion the range where you get appreciably better and better sound.

At $500 you are already getting a system that is not doing a whole lot wrong. But not massive output or deep deep bass.

By $2500 you're getting something that's doing very close to the full 17hz-20khz at output levels that will more than exceed just about any reasonable residential situation. And in fact your listening room is the bottleneck now.

Above that price you're paying for very boutiquey exotic stuff that can pull off certain tricks, very high levels of output, etc.

Those prices are very approximate and assume a well researched and set up system.