Garbage In - Garbage Out

 

Since some music sounds terrific, the not so much stuff can't be the fault of my equipment, but must be the recording itself.

Not sure how you make that leap. Interesting though. I wonder if it also works with broken clocks? Since its right to the second  twice every day, I suppose its a good timepiece. Maybe its the time that's just not right. So the clock really isn't broken. So I'll be happy knowing my clock is as good as any.

Well, I've been there with that kind of equipment. On some pieces it really shines. But the rest stinks. Usually a source unit of some kind. mine was a CD player. Some try to say its exposing a bad mastering  or bad recording. Consider this. most of the time its the same guy who mixed or mastered that great sounding song that also did the piss poor one too. Do you think he lost his hearing between those 2 songs? Do you really believe artists and recording companies pay people to do such poor work? Nah. Get another source I've been there and its not the music that's all bad. As I have climbed up the ladder to better equipment the music sounds better. Sure, some sounds better than others. But overall, I don't have many real dogs...well except that Edgar Winter "White Trash". You too can cut down on the dogs but I suspect your source player is not pulling its weight. Just a thought

OK, let me clarify my statements. The OP describes "tracks" as sounding great or sounding poor. I listen to albums. so to say one track sounds good and the next bad seems wrong to me. But I have been in exactly that situation and it changed with an upgrade to a belter CDP.
I also notice one poster who says its preposterous to say that a great system will make anything sound good. I agree. That's why I mentioned the White Trash album sounding bad. And I agree that there are different levels of production. I look for RL in the dead wax because Bob is very good at  mastering. And I understand good better best. 
But as I read the OP post it sounds as if half 0of the music he has sounds "limp". I take that as sounding bad. I have some bad sounding albums & CD's. But they are a vast minority. But it wasn't always that way. I have music that was unlistenable that I now listen regularly. What happened? I have been building this system for years. And as it has developed, more good sounding music has emerged. Is it all meet the TAS list of must haves? NO. But I love the music. And most a'phile music IE female vocals and a lot of jazz leave me wanting for something that moves me. 
It comes down to a matter of measure. If you don't mind having a system that only half the music sounds listenable or reasonably good then that is your choice. I won't have that system. I've had it before and moved on. But I had to satisfy me, not you, and vice versa.
BTW I am also a musician who has played for 50+ yrs so I have an understanding of what music should sound like.
Alums that sound good
"Will the Circle Be Unbroken" Nitty Gritty Dirt Band & Guests
"The Wall" Pink Floyd
"Waiting For Columbus" Little Feat

Can't think of any particular songs. Depends on my mood

I guess under the scenario you lay out I'd have to agree with you about poor recordings. But I don't really expect mono records from the 50's to sound good anyway. It really has to get towards the late 60's before you start getting reasonable quality. But people then weren't audiophiles. They marveled that they could have a recording at all. They didn't have the equipment back then to make great sounding recordings. Remember, stereo didn't arrive until 1958 and it was in its infancy. There is a lot of back story there as well, ie great depression & WW2 had made technological shifts to survival. Music was a luxury item. 
Another is Phil Specter's "Wall of Sound" Don't listen to it on a good stereo. It was made for AM radio. So that takes care of a lot of the 60's music, at least most of the R&B. maybe its because I lived through this stuff that I don't have much expectations. The times have changed a lot
The way music was played live was different too. Nobody ran everything through the board with live music unless you had a large venue. Everyone played straight out of the amps and the singer had a mic. 1000 and 2000 watt PA's are not rare today. I was lucky if I had 150 watts to sing through back then. Spring Reverb were used  til later 60's. Sure, the recording co's ran through a big board...maybe 12 channels. But a lot of early stuff you listen too was recorded with 2 mics IIUC. 
I started not to reply but it was a good walk down memory lane (-: