I also thought of going the SSD route at first. Eventually I preferred to try my luck with the CF as I found many negative references about the SSD on various forums (not only Jeep forums, but also forums for other Dodge and Chrysler models as well).
My main concerns about the SSD were:
a) In order for the SSD to properly work with the device, it must be supported through the BIOS; and this isn't the case with Mygig (which runs on a version of QNX, a Unix-like OS). If I recall correctly, someone reported he had to wait for almost ten minutes for his device to boot after power up. (But I'm not sure if this was a BIOS related issue).
b) A large SSD, ie a 64Gb drive as you mentioned, would hold a very large number of music tracks. Mygig has neither the processing power nor the interface to handle such a large amount of data. It would take ages to browse through your music...
You would also have to find a PATA SSD which is extremely rare (and from an unknown manufacturer), as most mainstream SSDs run on the faster SATA interface. And I'm not sure if it is possible to use a SATA SSD attached to a SATA->PATA interface and fit all these inside the Mygig enclosure.
But don't let me discourage you!
Do your research and let us know how it goes.