How to find the good CD recordings?

I’m not a big fan of Geddie Lee’s voice, but I know there are lots of discussions over the merits of various pressings and I have a couple of the records here somewhere. And Floyd- well, Wish You Were Here and Dark Side are obvious favorites, the latter having been done with Alan Parsons. Back to your original question about production values, I’d say yes-- those bands probably have better sounding recordings than Zep did. I think the Stones (and I’m not a great fan of theirs either, though I liked the Mick Taylor era best) had some really awful sounding recordings when they were at their peak. Sticky Fingers, Exile, etc. I have an early stereo UK pressing of Let it Bleed that sounds great, though.
Thing is, a lot of the standard Redbook is pretty much bargain basement pricing and going down, while SACDs and some of the fancier CD issues command money. I think you could spend wisely and buy a whole lotta CDs for your money these days. I bought a bag full at one of the local stores- not necessarily knowing what all of them would sound like, sonically. They were cheap enough-- 3-5 bucks a pop that it was worth just grabbing them. For those that suck, I can simply sell them back to the store for a buck or whatever --
FWIW, the "loudness wars" is all about having everything at '11'-- it's a certain style of recording/production/mastering- so there is no dynamic range, i.e., contrast between loud and soft. As a result, what you hear is very flat in a dimensional sense, with little life-- kinda dead sounding, b/c everything is brought up (or down) to the same levels through the use of compression. 

whart, I also like the older Zep and lean strongly toward their blues based songs. So strongly in fact that I've gotten into the blues that inspired them and have collected many of the blues songs they, well, ripped off. Unfortunately all of these blues songs I collected via iTunes which I only recently learned and now recognize are of fairly poor quality.

I really, really don't want to go down the rabbit hole of collecting blues 45s (or earlier) so I'm not even sure how to go about getting quality recordings of that music......which was as often as not produced on old equipment and with fairly poor quality.

I have enjoyed going to Clarksdale, Mississippi (where the fabled crossroads are) for their spring blues festival. There are stencils of Robert Plant's face spray painted all over Clarksdale.

A lot of the older rock recordings are not very good.  I am a huge Zepplin fan and I was always surprised by the poor quality of their recordings.  A lot of it is due to the compression of the dynamics which sucks the life out of recordings.  Even current groups don't get it and still use way too much compression.  You can only do so much with re-mastering and really have to get back to the original mix.  That being said some of the latter recordings of Bonnie Raitt, Rosanne Cash, Patty Griffin, Wailin' Jennys, etc. are well done.  I always look for the recording engineer as a hope of a good recording. 

That’s why it’s called Loudness Wars. Because when they overly compress the CD dynamic range they can make it louder. So a clue that a given CD has been overly compressed is often that you have to turn the volume down. Whereas for CDs with relatively high dynamic range you might find you have to turn the volume up.

@n80- I too am a big fan of blues, both the old rural stuff (I buy transcriptions, I don’t play 78s) as well as the electric era (from Chicago ’50s era to British blues revival). If you like crushing blues rock, try Barbed Wire Sandwich by Black Cat Bones- it was sort of a crude precursor to Free, without the vocal quality of Paul Rodgers, but it’s a killer. (I have a couple CDs of it, the original vinyl pressing is pretty big money- I’ll try and figure out which one I have that sounds better). Free’s first album, Tons of Sobs, is also a great, great blues rock record- Guy Stevens at Island had a very loose hand, and the band didn’t sound very "produced." Not sure about CD versions of that, but before they morphed into that ’Bad Company’ sound, they were first a monster hard rock/blues act.
That’s cool that you go to Clarksdale (ville). We passed through a couple years ago on our way down to Greenwood, Miss. Despite the bleak history of the Delta, it was surprisingly lush and beautiful- and people couldn’t have been nicer. I did have to ask what ’come-back sauce’ was. :)
PS: the Barbed Wire Sandwich CD that sounds better than the other one I bought is BGOCD916, allegedly mastered from the tapes. Not too pricey. Check Discogs for the BGO copy, circa 2010, i think. That may lead you to Leaf Hound, Growers of Mushroom, which has a very Zep 1.5 sound. The original vinyl record goes for astronomical money. I think the See for Miles CD was made from the tape. I can check.