HI JT and Welcome!
"Radio Shack amplifier Model: 15-2507." You may get better results if you use a"better", lower noise floor amp, and add a rotor for more precise aiming.
1) I don't understand why 36, 46, and 55 come in so well while WBTV doesn't. These towers are practically right next to one another and WBTV puts out more power.
Think about that, I won't comment as I used to work there.
2) The signals for 9 and 18 are stable and not pixellated even in the 60% range. Channel 9 can drop off the Charts when weather is bad, but 18 seems to be stable all the time.
Where you are, there are some terrain issues that affect reception, even tho 18 and 9 are side by side..Plus, re-aiming the antenna with a rotor should help.
Some areas of Hickory are on the fringe our our coverage area due to distance and tower height.
3) will these stations boost there transmission signals as digital conversion becomes more mandatory? If so when will this occur? And how much more will they be boosted?
No, we're all at fully liscensed power..WBTV,WCCB, and WSOC all run 1 megawatt
the maximum. (unless there is a transmitter problem)