For the image quality concerns you've expressed you would do best with a full frame, so K-1. But that doesn't meet your budget concerns, so we're looking for best image quality for a cropped sensor body. As a general rule the later the body was released the better the image quality from the sensor. But that doesn't always hold up with the updated versions, like the K-5 II which has the same sensor as the K-5, which is almost as old a design as the one in your K-r (though a little bit higher resolution and quality and an unquestionably good one).
I agree that resolution will help for landscape work. It's helpful for most purposes, actually.
Personally I find an articulating screen invaluable. I shoot at knee height and at full arms-reach overhead every day.
High sensitivity quality is always good, but doesn't usually matter as much for landscape work, where tripods are most common, as for other kinds of photography which are more frequently handheld.
In short, the K-3 or K-70 would be very good upgrades for your needs and as body-only options they are rather affordable. If those are too much of a stretch then the K-S2 would be a good option (I love mine) but you might want to make do with the K-r until you can get one of the others.