At the time, I had a pen pal whose tween daughter was the same way. The thing I most remember is that her daughter had spent almost $100 just on trading cards associated with the movie.
Never saw it myself.
I was also going to mention “Xanadu” and “The Last American Virgin”.
Transformers: The Movie (the 1986 animated one) is a crap movie by any objective standard, but has a kickin’ 80s soundtrack.
Seconded.
“Mondo Cane”, parts 1 and 2 both, are available on Netflix. Your post prompted me to bump them a little higher, so I guess I’ll find out how bad they are. 
There was an atrocious early 1970s teen-oriented movie called “Friends” that used to air on Lifetime when that was a brand-new channel. It also had a terrific soundtrack.
I never had any idea what that movie was about, but “More” was my parents’ “song,” so I heard it a lot of times around our house (and even learned to play it on our electric organ when I was a kid).
Now that they’re both gone, on the rare occasions I hear it I get a little sad.
My vote goes to Batman Forever. Barely passable movie, but a great soundtrack. Hold Me, Thrill Me, Kiss Me, Kill Me. The Passenger. Kissed by a Rose. The Hunter Gets Captured by the Game. There is a Light. Bad Days.
It’s better than any of the Michael Bay joints, and for a kids movie made to sell toys standards it’s pretty top tier.
While I disagree the movies are bad, I don’t think anyone can say the sountracks to Star Wars Eps 1-3 are anything but more John Williams brilliance.
My nomination. Between remembering the advance hype and having, once upon a time, read My Indecision Is Final, I’ll still automatically give it another go whenever I come across it on television. Perhaps once a decade or so. It surely really can’t be as bad as I remember.
It always is. Weirdly, even moments that I remember as being quite good from earlier viewings always turn out to be false memories.
Yet that Bowie title song …
I really liked the soundtrack to I <3 Huckabee’s. It had a sort of hipster, indy sound to it, a type of music I don’t normally enjoy, but it was still excellent. The movie was complete slug shit.
I first thought of Barry Lyndon, which I agree was more of a score than a “soundtrack.” However, I loved listening to it, but in my mind it was a dumb movie (Sorry Stanley Kramer).
No one has mentioned (at least that I saw) Don’t Stop the Music Definitely a foul movie and granted the music was the tackiest of disco, but it was fun. Also the music was a rehash of absolutely every Village People album ever…but it was fun.
Also Darling Lili staring Julie Andrews and Rock Hudson is a good example of this thread. Everyone agreed the movie was painful but if you liked the music of the WWI era, it is quite good.
OK…one more and probably not a “bad” movie, but it was well outpaced by it’s soundtrack. Thoroughly Modern Millie.
*Xanadu *has the distinction of having the only Olivia Newton-John songs I can tolerate.
Never saw the movie, never want to. I don’t want to ruin the soundtrack. 
Oscar nominated, no less.
Casino Royale is my go to answer for this type of question.
Hot Tub Time Machine is 1986 pop encapsulated.
The Shep Pettibone Bizarre Love Triangle remix is my dog’s favorite song. 6 minutes of being chased around the back yard totally makes her day.
That reminds me of Rock ‘n’ Roll High School, which probably qualifies for the thread. I can’t say for sure, though, as I haven’t seen it in decades but I do remember it being terrible.
“In XANADU, did Newton-John, a disco roller rink decree…”
“…Where Gene, the Sacred Hooffer ran
Through sound sets measureless to Man
Down to an unforgiving sea.”
I’m a sucker for the old Olivia stuff, especially from the mid-late 70s (even though I wasn’t born until 1975).
Spawn was a very dumb movie, but the soundtrack is a great collection of 90’s electronica. The Crystal Method/Filter collaboration “Trip Like I Do” is one of my all time top 5 songs.
Manos: The Hands of Fate. The soundtrack is the best thing about the movie. Especially the end credits theme Forgetting You. It’s quite haunting.
I watched Part 1 tonight. That could best be described as “National Geographic on acid”.