Aniesen
There is no fair comparison, as the 1C is only half of the 2CE. The 1C is the 8" woofer and the tweeter, while the 2 models all have the woofer and tweeter as well as the 10" accoustic coupler and a 5" midrange. Having heard them all, and having owned Models 2C, 2CI, 2CE, 3, 3A, and 4, I can't say enough good things about the 2CE.
But back to your original question, the comparison. The midrange, or lack of one, makes a big difference. Most people say that 80% of the listening we do is in the midrannge. Thus having a speaker in the system that is devoted to the midrange adds definition and nuance to the overall sound, and it also lets the other speakers concentrate on a narrower range of the audio spectrum so they can reproduce more precisely. Having the 10" accoustic coupler fills out the bass and gives the speakers body and bottom. The 1C is a great 8" 2 way speaker, but it can't compare to the 2s. It's like minor league versus major leage baseball. They're both playing the same sport, but one gives you so much more than the other. Save your pennies and buy Model 2s. I listened to the new 2CE Sig IIs, and they are wonderful, but my old Model 2s were great, and my 2CIs had so much soul. You can find used 2CEs here on Audiogon for $500-$650, so if it's achoice between buying new ICs or any used Model 2 buy the 2s. You'l be sorry if you don't.
Good Luck, MJWPicMan.