Can a great system make a mediocre recording sound good?

As waytoomuchstuff sez... Find a balance. Seek friendly improvements. After all, didn't you fork over all that cash to better enjoy the music?

With an accurate system, you have to get to your head into "context" to enjoy them.  Many recordings of particular era are limited by technology and share a family sound- say English recordings of the 70s and early 80s or US recordings of the 60s/70s or 80s.  Motown records are a great example of a shared sound.  There are some notable exceptions of the era, records that sound very raw. and unprocessed.  Satana's first album comes to mind on a good system!  

I notice the differences in recordings much more as my system improves. Take the good with the bad. Doesn't mean a bad recording isn't an awesome song, concert etc. just enjoy that your ears can hear the difference.

@telemarcer

I notice the differences in recordings much more as my system improves.

Better systems tend to have wider bandwidth, but mediocre recordings don't, and here lies the problem.

Playing back recordings which favour the midrange ie most pop, on a wide bandwidth system is unlikely to lead to satisfaction. Not when the sound is getting pulled apart and brutally exposed.

Those recordings tend to sound better on systems which favour the midrange.

I suspect this is also part of the reason why small speakers like the classic LS3/5 remain so popular.

Virtually any recording will sound good on them.

Depends on the listener  .