I'm going to make the assumption that this wagon I'm looking at has a stock Ford stereo with factory speakers in the dash (Crutchfield says 4" speakers will fit) and out back (Crutchfield says they are 6" x 8").
I want a factory looking deck (lots of black, little if any silver, green or blue lighting, 2 big knobs would be nice, retro > *) with either MP3 CD playback or a front-mounted auxiliary input (for my 1GB Shuffle), but there's no way to do that with any single-DIN sized Ford offerings. I'm looking at 3 stereos to put in, all in the $80-$120 range.
Pioneer DEH-1900MP...this has green button illumination and a white LCD display
Kenwood KDC-MP235...red button illumination, light blue LCD display
Kenwood KDC-MP2035...blue knob illumination, red button illumination, light blue LCD display
I can't find many differences between the two Kenwoods, maybe $5 in price if that. I'd probably take the 2035 over the 235 since it has less red. I don't like red lights but blue is ok, so that's a trade-off, but if the rest of the dash lights up green like I think it would, I'd want that Pioneer. All three of these have an input on the face AND play MP3 burned CD's, so even if I forget my Shuffle, I can use CD's stashed in the visor wallet or glovebox or whatever.
As for speakers, if I go with the Pioneer deck I'll get Pioneers, and likewise with one of the Kenwoods. Are the dash speakers difficult to change out? I assume dash pad removal is required? Might be a good excuse to find a very nice blue dash pad to go in. Am I limited to 79-87 CV's and GM's for this part? Or will 88-91 pads fit, too? How about Town Cars, do those pads interchange as well?