I am debating converting my mp3 collection to ogg. Are there any real advantages to it?
I don't think you'll gain much quality unless you rip directly from an audio source (a CD) to OGG.

In response to Kujila
Well, I know you cant gain quality from a file aready ripped. My question was more on file size, stability, portability, and lifespan.

Unfortunatly my mp3 player wont play OGG, it will play WMA though. So I probably wont switch over. But I have not yet decided.
No real advantage, no, unless you need to convert them to OGG for some reason. If it works as MP3, keep it; you'll only lose quality through the conversion anyway.