I'd say the availability of millions of used Kodak slide projectors bears witness to their ready availablity at AV dealers, camera stores, and discount houses, very few of which carried Leitz projectors. This has little to do with value relative to other brands.
IIRC, the Pradolux RT-300 mirror that bounces the light 90 degrees from the lamp through the slide actually passes IR and UV light rather than reflecting it, resulting in less damage to the projected slides over time.
The Leitz projector lenses are much better than the Kodak lenses supplied as standard, even the fixed focal length Kodak lenses. The common Kodak zooms don't come anywhere near telling you what's on the film. Buhl, Schneider, and others made good projector lenses that decent AV setups used in preference to the standard Kodak lenses.
The Kodak Carousels that I've used over the last 40 years also have a strong propensity to go forward the first time you hit the reverse button on the remote control. So you often have to reverse three times to go back one slide.
People will almost pay you to take away their used Kodak Carousel projectors at this point. AV departments are throwing them away. (Power corrupts. Powerpoint corrupts absolutely.) Try walking off with someone's Pradolux/Pradovit and you'll find out about perceived value.
Standard equipment Kodak Carousels aren't 'bad' per se, but Pradolux/Pradovits with a Leitz lens project a clearly superior image.
There are two kinds of slide projector lenses, flat field and curved field. Flat field are for glass mounted slides. Curved field lenses are for glassless cardboard or plastic mount slides. Both Kodak and Leitz curved field lenses have a "CF" designation on the front bezel of the lens.
My son has a Kodak Carousel and Kodak 102mm CF lens that I found at a garage sale for $5.00. He always asks to use my Pradolux and 90mm Colorplan CF.
Lee