You can just go straight from SPC to mp3 with foobar. It's really fast. Get foobar 2000 (
http://www.foobar2000.org/?page=Download) , get the foo_gep plugin (game emu player) (
http://www.foobar2000.org/components/view/foo_gep) which allows foobar to read the spc's, then you also need the lame mp3 encoder (
http://www.rarewares.org/mp3-lame-bundle.php). Get version 3.98.2, the best current version. Just put the two plugins in your foobar components folder, open the spc's, select what you want to convert, right-click, hit convert "..." , tell it where you want it to save and in what format, and there you go.
After you do it a couple of times, it should only take like 5 minutes from clicking the link to download the spc files to having an mp3 set of them.
Let me know if it doesn't work for you. You can also do it this way with any other file foobar will open, like FLAC, for instance, or NES (.nsf), genesis (.vgm, .vgz), gameboy, etc. You can do this with playstation music files as well, but you need the foo_psf (
http://www.foobar2000.org/components/view/foo_psf) plugin to do it.
You can find lots and lots of emulated music files from the older systems (i.e. before PS3, XBOX360, etc) at:
Zophar's Domain Music (
http://www.zophar.net/music.html)
vgm.hcs64 VGM archive (
http://vgm.hcs64.com/)
Project 2612(genesis/megadrive) (
http://project2612.org/list.php)
Or, alternatively, you could use my own little custom google search (
http://www.google.com/cse/home?cx=005506110847696921220:yp9c31poyds) that has those sites and GH as well as this forum on it. I've found this works much better than the built-in search function in the forum.
*edit--Lens, I use winamp sometimes for .vgz's that foobar won't read, but I don't like to use it because the mp3 out plugin converts to mp3 just fine, but drops all the tags. I could be doing it a stupid way, though.