In reply to LeeWood:
Hi Lee. Sorry I have no idea whether cat lenses for DSLR are still on the market. I do use a rather large one for my astrophotography, but that is linked to a specialised astro camera. Yes you are right the doughnut highlights only occur with bright specular reflections.
As regards the benefits of cropped format, they are cheaper and lighter than full frame. Not so good if you like wide angles, good news if you like teles. I use an APSC Pentax body (K3ii) with my Pentax lenses and I really like it. APSC gives you 1.5 times the focal length. Micro 4/3 cameras like Panasonic or Olympus give you 2 times the focal length.
As Kevin says, if you were going to keep the Pentax lenses then a Pentax APSC DSLR is an obvious choice. However if buying used watch out for older models which suffer from the "aperture block failure" (says the man who has a new aperture solenoid on the way to attempt open heart surgery to fix a Pentax KS1).
Good luck
Paul