I had Ford C springs on my 98gt and I was told I dont need C/C plates. After driving it for a couple of months I did notice the tires wearing, then I purchased the the C/C plates.
With Fords liberal specifications for the Mustang even a Car with Factory stock springs can benifit from CC plates. I hear most say if you don't get more than an inch or so drop from your springs then you'll be ok. Maybe so, maybe not, as mentioned, depends on your car.
If you want to get a real good alignment and not just meet the Ford specs go ahead and spring for a set of plates. When I checked my Car before I installed the MRT springs the camber was .25 degree on the left side and near 1 degree on the right, the caster was way mismatched too plus it wasn't near enough for a really good turning performance driven car.
Sounds good to me. Thanks for all the info. I think for now I am going to do the install\re-aliment and go from there. I will get the plats soon I bet. I got a nice new slotted rotors ;-)