Most mirrored OTAs wll have issues with mirror movement because the mirror cells cannot rigidly lock the mirror in place without inducing stress into the mirror. My limited experience with modified Cassegrain designs suggests that they are difficult to collimate. Overall, IMHO, their advantages (in the 14in size range) over an SCT based design are minimal. Additionally I would research Newtonian astrographs before making a final decision.
I can't say your experience matches mine, though I have not owned scopes larger than 12.5" so it's possible things are different in 14" and 16" sizes. I find that CDK's are actually quite easy to collimate; like an SCT you only need to worry about the secondary. If the primary is off (or the secondary is out of center) the only symptom is imperfect field illumination, and a flat resolves that.
I have not noticed significant collimation issues from the mirror mounts or in the OTA on either of the two 12"+ class telescopes I have owned. None.
Advantages over a 14" SCT from an iDK/CDK? Several.
- Typically better cooling/faster equilibration due to open tube design /
- Larger unvignetted field of view
- Often more back focus available
- Less susceptible to dewing
- Larger flat field (than either a Celestron Edge and much larger than a Meade ACF)
- Slightly faster than an ACF or a Celestron with dedicated reducer
I'm not saying those differences are necessarily worth the cost; that's up to the purchaser. The advantages are more than minimal, though. As far as imaging Newtonians... In this size range wouldn't you need to have something custom made? Including the Wynne corrector? ASA tops out at a little under 12". I suspect it is difficult to make something stiff enough at a reasonable weight to handle a heavy camera hanging off the side of the tube once you cross a certain size threshold. That sort of load not attached to the back plate must be a real challenge. Maybe you know of some 14" class Newts? Everything I could find was a Cassegrain of some sort--Officina Stellare (various designs), Starizona Hyperion, AG Optical, PlaneWave...