Any amount of compression is almost universally going to make bad rooms sound worse.
Just to expand on this. The reason this is true is because compression will make any ambience that has been recorded along with the sound more apparent, especially at fast attack settings.
Also, along those same lines, if a sound has been recorded in a reverberant space, along with natural reverb, it will make that reverb more apparent, which in turn will push the sound further back in the soundstage.
Considerations, considerations...
One way to really hear what Attack and Release do to the sound is to do this:
Setup a compressor on a track with the following settings:
Threshold: all the way down (i.e. in the direction so that it compresses basically everything, if it is in dBs, then go to the lowest it will allow, like -50dB)
Ratio: the highest
Attack: fastest
Release: fastest
Now, at this point your track will likely sound very quiet and pretty well destroyed, but we're not going after quality, we're after extremes so we can actually hear things in not-so-subtle ways.
What you want to do now is setup a loop of say 4 bars, and hit play in your DAW. Now, slowly start increasing Attack. If you have a rhythmic material for this (like drums), even better. You should now start hearing how the attack transients are starting to poke through. In crease Attack as far as it will go to get a feel of what gets through and by how much. Again, a drum mix (drum loop, or a submix of your drums) would be best for this, because you can hear the difference in transient times between the kick, snare, and hi-hats for example.
Now decrease the attack time again, but set it so some transients poke through. Now start increasing the release time. Listen.
Enjoy.