JW, it really depends how much colour you shoot, in my opinion (and as photoncatcher implied).
My own take on this is that the price difference is really small, when you consider the benefits of the newer lens. Besides the advantages of being newer (remember these are all-mechanical lenses that can have quite some history on them if you buy them used), the KLs are improved in various ways. The coatings are better, and the lenses are generally a touch more contrasty and neutral in tone (I suspect that lower dispersion glass was used in the newer designs, anticipating their use on digital backs which really require low dispersion). Mind you, I never got to compare a new C to a new KL....
So that is just my own take, after going through all kinds of RB lenses from pre-C to C to KL. Eventually I just did the math and concluded that the KLs are worth the modest premium. I mean, all the mammies are the cost of peanuts compared to the hassies, that's the way I look at it.
However! ...if the price difference is significant to you, then sure, go with the C and be happy. Don't let the extra cost prevent you from enjoying the field of view. Just be sure to hood it judiciously, that should take care of most of the difference in terms of coatings. If you shoot b&w then minor differences of contrast will be naturally accounted for in your processing. So, if you shoot mostly b&w, then the C/KL difference will not be large. I shoot quite a lot of colour slide and also am fairly reckless in terms of including the sun and other bright sources in my frame, and I also do quite a lot of IR, so... the KLs and apo-thingies are for me.
