I do remember sitting at the kitchen table one Saturday morning and deciding to go shoot the Grand Canyon. I tossed all my gear in the pickup and started up I17 getting to the canyon about 5 pm. Shot the sunset - but my brand new K5 pulled up lame (the mirror motor went out - warranty), so I just continued shooting with my old K100D. I processed everything and put the images on a thumb drive, plugged it into the large screen TV to flip through them. The K100D images held their own against the K5. I learned right there that old cameras are not necessarily inferior to the new ones.
I shot with the K5 for years and even picked up a really inexpensive K5IIs on closeout. My son now has the K5 down in Florida. The K5 to me is the watershed body, where everything just went right. I upgraded to a K1 when I retired, with the reasoning that I wanted more star color in my Milky Way images. Why drive up to 3 hours one way, and shoot for 3 to 6 hours (12 hours total round trip) and not get really what you want in the images.
The K1 came in the mail. I unpacked it, picked it up, and instantly realized that the K5 was an absolute joy to shoot with. Lightweight and with a very easy straightforward user sense to it. Not that the K1 is bad, it's heavy (and I quickly became accustomed to it), a beast of a camera (took me a bit to get all the controls down, get it set up - and figuring out the differences between the K5 user interface). Actually, there are times I forget and revert to the K5, and whatever is not there.
It's funny, with the K5 I struggled to get the star color I wanted, but the landscape element was drop-dead nailed. With the K1, the sky is nailed with the colors I want and expect - but the landscape element, I now struggle with - getting detail, shadowing low noise clean images. My expectations are waaaay higher, and I'm shooting much in darker environments. A little light works wonders.
My K100D would never give me the same images I'm now capturing with the K1 - but it and the K5(IIs) still has a place on the shelf and I get out with them from time to time. In terms of build quality - Pentax has always had it, and never really lost it - well in my opinion. My right arm is slightly longer than my left, from carrying the K1.....