Evening, and Welcome to the Forum!!
I just turned 71, so we are both getting to be as old as dirt. I had (well still have a K5IIs) that I love - just drop-dead easy to pick up and go shoot with. Literally, everything I really needed and wanted, well except - I like to shoot at night, the Milky Way over large things, mountains, valleys, etc. My one single problem was getting star color in the milky way core. The way to do that was with more dynamic range from a full-frame sensor - the K1.
I thought long and hard after retiring on this - larger, heavier, more $$$ and also needed a new len$. Since I was driving 1 to 3 hours to get to where ever to shoot for several hours, it was worth it to be able to capture the images. 5 years ago, I upgraded, and yes, I'm getting the star color in the MW core now. Where I go is so dark that the starlight casts my shadow on the ground - so I'm pushing the camera and lens to their limits. On the other hand, the K1 is such a beast that other than MW shooting, it's a lot of overkill - well at least for me. 4 to 5 minute exposures just to be able to capture some good definition and details in the foreground landscapes. Also, the K1 is probably my last camera body - it's that good. The articulating screen is now an ABSOLUTE must if I were to get another camera body.
The bottom line is that, there is no perfect answer to your predicament.
The K3 is extraordinary that good too. It's so good, that it has a thread here on the forum with 4million views and about 100K individual posts to it (
you will come across it). I think that the bottom line is - after Parallax's questions, is there any image that it can't capture for you? Is there a limitation with the K3 to prevent you from being able to capture a particular image?