Tommie,
If you are wanting to listen ad-free without audio ads and pop-ups, you may want to consider signing up. However, if your main motivation is increased sound quality, I'd encourage you to wait until around early June. Right now the stream will sound the same either way.
Around that time, we are planning on making a variety of updates including better quality sound. Free listeners will hear slightly better quality (but still in mono), while VIP members streams will be in MP3Pro stereo at approximately twice the quality but at the same bitrate as normal. Actually, I'm hoping that Live365 will eventually make stereo MP3Pro streaming the norm across the board for all users, not just VIP members. That's their call though, not mine.