MD user in California
I've been using MD for over 5 years. I have a Sony MD Recorder head unit in my Honda Odyssey along with a 10 CD changer. The great thing about MD is recording old vinyl. It's much easier than recording to computer through sound card and then editing wave file. With the Net MD Walkman, getting tracks from computer (wav or mp3) is a snap and if I just want to record one song to listen to in the van, I don't have to waste a whole CD.
Yeah, MD is a proprietary format that hasn't been as successful as CD, but it has much more uses than 8-track.
Not sure if you can replace the head unit in the 323 but you might want to try this if you have a portable player
http://www.compusa.com/products/product_info.asp?product_code=286756&pfp=SEARCH
It's not the best sound but I've had decent results in my other vehicles.
I was considering Phatnoise, but the initial outlay cost ($900 + install) is a bit steep considering that those hardware prices should drop like a rock within a year or so.
If you can replace the head unit, that would be the best way to go. Even IF the format decreased in popularity over the next 2-5 years, you already have the components to get music to MD and play in your vehicle. It's not like you don't gain anything from having a MD system in your vehicle.