I was going to say Dorset but Tim beat me to it. I was honestly a bit disappointed by the old 9 at DFC, after I had long wanted to give the course a try. It's not bad by any stretch, just not hugely memorable.
New England has a bunch of courses like this, with a good old nine and a new nine that is less than amazing. Biddeford -Saco (Ross + Cornish & Silva), Brunswick (Stiles + Cornish), Cape Neddick (Ross + Silva), and Waterville (Orrin Smith + Cornish) in Maine, CC of NH (Stiles + Mitchell) and Kingswood in NH (Ross + Tom Clark), CC of Barre (Stiles + Hurdzan) and St. Johnsbury (Willie Park + Cornish) in VT. Crumpin-Fox in Central Mass. would be another, but the two nines were within 10 years of each other, under the same design flag, with RTJ doing the first nine and Rulewich doing the other.
All of these are worth a play, with expectation of a less-than-spectacular compilation or tie-in of two nines.
How about the Broadmoor (Ross) being split into two lesser (but still pretty good) courses by 18 RTJ holes in the 50s/60s? Not sure if this fits, as it's a resort that no doubt wanted more golf without there being a clear favorite course that everyone wanted to play.