georgem is correct. What we generally refer to as a "California Coupe" has no soft top, top bow / frame mechanism, no rear 'top well' to store a top in folded down position, or the hinged 'cover' that goes over the soft 'top well' of a normal roadster. There is no provision to easily add a soft top to a CA Coupe. Instead, it has a back seat (for extremely small people, with even smaller legs).
A couple of photos here show a normal roadster with folding soft top (green car - two different green cars actually)... the other photo shows the rear seat of a parchment interior CA Coupe, taken with the hard top on... it's the best I had.
A true CA coupe is as described above, with a back seat / no provision for a folding soft top. I've seen a couple of true 'soft top delete' cars though too... they have everything you see in the photos of the green cars pictured, except the soft top and frame (which you can't see in the photos, as the top was all the way forward with back window folded towards the front when the photos were taken). If you have one of those, it's fairly easy to buy a top frame and soft top and install it. A friend of mine is currently restoring a 230SL and that's been his dilemma. He thought he had a CA coupe, but when I saw regular parcel shelf in the back instead of a rear seat and the 'top well' and hard folding cover were there, and after confirming with the build card, we realized it was a car that was just ordered without a soft top. Not sure how common that is.. it's the first one I've ever seen. He's since sourced a frame (almost $2500, well used) and will be getting a soft top for it too.
Value... It's hard to say, as everything seems to be changing so quickly these days and prices range greatly. All things being equal, I would think a 10% deduction is low... it may be more about just finding someone who wants one more than value. I think they take a bigger 'desirability' beating in the U.S. than in Europe. The European folks can chime in here. Whenever I see them on the market here in the U.S. they tend to languish for a while and don't seem to be snapped up real quickly, but that's my anecdotal thought, I've never put a calendar to it.
Personally, I prefer the look of the W113 with the hard top on and I don't like to be out in the Summer sun so much, I simply can't drive on Summer days with the top down after an unfortunate case of heat exhaustion a few years ago... so, I often leave my hard top on all the time, so a CA coupe would probably suit me fine. I think I'm a rare case, most people looking for Pagodas that I talk to won't even want to entertain the idea, no interest, no matter the price. The photo of the CA coupe here is a car I looked at in Kansas last Winter, a 280SL. I ultimately passed due to condition and other factors... non original color color change for one. It was offered to me in the high twenties. I learned that it recently sold on eBay, within the past few months for high $30,000s. Oh what a difference a year makes.
