How do Klipschorns compare with modern designs?

I too am a horn fan & love my vintage 1978 Klipsch's despite the drawbacks (horn coloration - true - but they're real picky about signal quality being fed into them). Transparency isn't the greatest but is still pretty decent, although they are *very* revealing of micro-details & will absolutely show you every little change that you make in your rig. Regarding dynamics they really shine here - rivals that of live performances. If you like to tweak there are numerous things that can be done to enhance these magnificent beasts (yes they are large & heavy). You can even use them without room corners if you fabricate some "artificial corner" panels such as Paul K. himself does. Or get the Belles, which look somewhat better than the K-horns, or the budget model LaScala is another alternative.

Jm I realized that I neglected to answer your stage & image question. Results in that regard are mixed & somewhat confuse me. Depending upon the source equipment & even moreso the associated cabling, I've sometimes had poor staging & at other times it has been unbelievably huge, like I moved the speakers right out of the house & into the front yard or somesuch.
However I do not have the corner horns, but the Belles (which use the same crossover & drivers & even a folded horn bass cabinet) but are made to work without the corner. So of course mine are not positioned at the room corners, they're practically nearfield at about 7' distance from the listening position & dividing the long wall into thirds. This works out well for me because our living room arrangement doesn't allow for speakers being pulled well out into the room. Spacing from the backwall is at an angle & only about a foot or so away, not a good situation but I can get away with it because the Klipsch are designed to work close to backwalls. I realize that this layout hurts staging but it can still work very well with proper setup.