$7900 is a bit high for those miles, but somewhere around 6500-7000 would be a good price. Not great, but good. My HVAC control system doesn't work right either and the buttons are hit or miss. You can send them in and they will come back working properly for about $150 I think. I'm pretty sure it's just the connections behind the buttons wear out or come loose, so they don't work as well anymore. I know there was a thread over on Yotatech about someone taking theirs apart and fixing it up.
Not sure about the sound. The valve cover gaskets don't need to be changed unless they are leaking. Most people can get away with just tightening down the valve covers bolts and the leaking will go away for a while. But it is a good bargaining point. Basically check the rear axles for the seals leaking and the transmission fluid for the pink milkshake. Also check all aspects of the 4wd system. Check 4 Hi unlocked, locked, 4 lo and the rear diff locker if it has one. These years are notorious for sticking and it is a costly repair.
