I can't really comment on your film gear situation, as I have little background and experience in that area. But, like some others that have responded, I'll challenge your view of - and perhaps re-ignite your interest in - APS-C, assuming you still own a camera with that sensor format.
I shoot both Pentax APS-C and non-Pentax full frame bodies, and the only significant difference is which lenses to use for which purpose. A 30 - 35mm lens on my APS-C cameras fulfils much the same role as a 50mm "normal" lens on my full frame bodies. A 50mm lens on APS-C fulfils a similar role to a short tele in the 75 - 85mm range on full frame. Once you get used to the field of view each lens offers on APS-C, it's no less capable in most respects than full frame, and in some applications (wildlife and sport photography, for example) it can be better than full frame.
I say this with some confidence based on personal experience: my favourite camera to shoot with is a twelve-years-old Samsung GX-10, a re-branded clone of the APS-C sensor Pentax K10D. I choose to shoot with that more often than any of my other cameras, including my full frame Sony A7 MkII and Hasselblad HV.
And the image quality from modern, high resolution APS-C sensors is
incredible. You only have to look through the thousands of images posted on forums such as these to see what's possible. Any limitation is almost always the photographer's skill and technique, not the sensor size.
So, if you should decide to buy a K-1 or other full frame camera, that's great. I certainly wouldn't discourage you. But if you still own an APS-C camera, I'd recommend re-evaluating why you don't like that sensor format - why it doesn't work for you - given the above observations
EDIT: I wonder what you'd think of the Pentax Q7 that I also love to shoot, with its tiny 1/1.7" sensor? Yet I've taken photos with the Q7 that, viewed at an appropriate size (for example, filling the screen on my 17" laptop), are all but indistinguishable from those taken with a larger sensor DSLR. I'm not trying to convert you to the Q-series, but underlining the fact that sensor size, for the most part, isn't as important as some people think