I love my GR. It pretty much goes everywhere I go, and has been a great travel camera. I've had it for about a year, now. I love the ease of use, controls and image quality. I feel quite at home with 28 and 35mm focal lengths. If you're someone who is inclined toward 28mm and want an enjoyable, powerful compact camera at a decent price, I'd put the GR high on your list of cameras to consider.
In answer to your specific questions: 1. I don't miss a having an optical viewfinder on the GR. I do appreciate cameras with a good viewfinder, to be sure, but for this camera... I don't find it suffers in lacking a OVF/EVF. 2. I can't speak specifically about the K-5iis, but I've found the sensor performance is completely acceptable. Very good from 100-800. And good to acceptable from 800-3200. 3. I really like the image quality of the pix I've taken with the GR. Textures are pleasing to my eye. Metering is good and exposure compensation control is the best I've experienced in a digital camera thus far. The shot white balance is generally very good for skin tones (somewhat subjective, of course) but in photos where I've wanted to adjust it, I've found those files easy to work with (Capture One and Aperture).
All this being said, if I were considering purchasing a new compact camera right now I would be looking at the GR and be checking in with myself about my long time tendency to shoot with compact single focal length cameras (Minolta CLE, Contax T3)-- and then I'd take a close, serious look at the Panasonic LX100. That camera seems like a real strong contender for a powerful, take anywhere compact camera. And it has an EVF, even!