First off, if you're looking to skip folders from being scanned, put the .nomedia file inside the folder. Second, using my A500 for music has lead to several particularly annoying issues. Putting music in the micro SD card is just bad news. Very, bad news. My music players would pick up duplicate entries of the music files which is reminiscent to my problems with the original Google gallery. That app would pick up and duplicate entries in its cache when the micro SD card needed to be reloaded.
Lesson learned. Do not put music in the micro SD Card.
Cleaning up the crap takes a bit of time and effort, but if you've isolated your files in a folder, that's good. Rename your folder and put the .nomedia file on it to keep Android from re-scanning and grabbing those poor files. I then used Winamp to purge all the music in the library which just removes Android's internal mapping. To be sure, load up each of your music players and make sure none of the music gets picked up. Move your music folder to /sdcard and remove the .nomedia file. Reboot your device and then run a music app which should begin re-scanning your device for media.
Hopefully, that will tidy up your music player.
