C&C models 3.X in that it has positive AC values and positive values for saves. Where it models 1E/2E is in the fact that it uses what is referred to as "Iconic Character Classes" like were in 1E and 2E. Plus spells are written with an eye towards their 1E/2E versions.
Plus the overall siplicity of PC and monster write ups by default makes them look like 1E/2E character and monster write ups.
As for ease of use with 3E, I define it as easy. My approach is to strip away what isn't needed when I convert 3E monsters and classes. Whatever power, feat, or skill I want the creature or whatever to keep, they keep. It mainly means they can perform the feat or skill as if they are a "Prime", which means base TN of 12 instead of 18.
Converting stat bonuses. The quick way? Subtract one from the 3E bonus. IE +4 becomes a 3. A little longer way? Look at what bonuses are given in the C&C PH, or on the Giants Belt in the M&T for creatures with stats above 18.
I think this is easy. Far easier than converting 1E/2E to 3E, since you have to decide/work out skills, skill ranks, stat bonuses, add to their spell lists, AC, and decide on feats.
Spells can pretty much be used as is since you would presumably understand how spell saves work in C&C. The only other considerations is whether to classify it as Mental or Physical Primes. Even that is usually done for you. 3E WIS saves=mental saves in C&C. DEX and CON saves in 3E are Physical saves in C&C. Easy.
The only other thing is to change spell durations to the time increments of C&C. Not hard once you know what the two increments are.
So I think this is easy once you know and understand the rules of C&C.
If I were to simplify 3E? I did. I used C&C as my base line and have built up from there. Holds up just fine. Heck, when C&C doesn't have a rule I think is clear enough I still refer to my 3E books to find a rule that covers it to my satisfaction. Recently the rules for how armor bonuses stack and to determine what class scrolls are for. Modified to account for their being Druids, Runemarks, Illusionists, and clerics only in my game. I also use my 3E PH to illustrate what weapons and armor looks like, or my Paladium books.
Another cool website to check out for the C&C Netbook of Classes and other house rules and resources for C&C:
www.cncplayer.net