Need advice on XM Radio vs. MP3 Player

For a while I've been thinking about purchasing an ipod for use at home and in my 330 (by connecting it with an adapter hat uses the CD changer input). Recently, however, I've also started considering XM Radio. After going back and looking at some of the clean XM installs posted here I am very tempted. I know XM Radio and a portable MP3 player both have advantages and disadvantages. Ideally I'd like to have both. I think I'd use XM most of the time, but I'd like to be able to connect a portable MP3 player too. My question is this: Since portable MP3 players and XM radio both connect by virtue of an adapter that hooks into the CD changer harness (I have in-dash CD BTW), would it be possible to connect both. Essentially the XM radio would be connected full time, and so would a wire which would sometimes be connected to the MP3 player.What do you guys think? Perhaps I'm being gready and should just choose one or the other...feel free to give me your opinion about which you would choose.