The answer to the question is two-fold (plus a bonus).
1-The camera itself is a significant improvement over the K-3. Total resolution, dynamic range and ISO are improved.
1-However, if you have 70 lenses it's probable that many of them are older lenses, and these sometimes do not live up to today's expectations. See
here. That doesn't mean older lenses cannot be used, and in fact using them on a full frame sensor makes sense since they were designed for that. But newer lenses show significant improvements over older products.
In addition, if you own APS-C lenses (DA, essentially) then you might be saddened by the effective resolution on the K-1. Some APS-C lenses work perfectly well on full frame, others don't as they create black corners which cannot be adjusted in post-processing. This means you will use only the center portion of the sensor, giving you 16 MP (the same as your K-50). You will still have all the dynamic range advantages of the K-1, but not the full resolution.
The bonus is this : with the K-1 you ALSO gain a tilting LCD, superb AF, LEDs all over the place to work in the dark, pixel shift, the best ergonomics Ive ever seen, daylight screen adjustment, electronic shutter, night mode on the LCD, did I mention the ergonomics? I'm probably forgetting many things I love about the camera, and now take for granted.