"Here's one more question for ya'll in the know. If I pay cash to upgrade a full-Y fare ticket to business or first, will I get the extra Q-point bonus (25% or 50%)?"

if you pay the difference between Y and J/F, then yes you would get the bonus mileage.

"And if the answer to the above question is yes, any idea how much it costs to upgrade at the gate to business or F? (1/2 my flights don't even have a first class, let alone a business "

That would depend on the route. Just look up the F fare for the journey you want to do and subtract the Y fare from it to get the amount.

You can get upgrades using upgrade credits , ( either the 4 awarded per 10,000 miles or by purchase at around $35 each ) using 1 per 500 miles. In this case you would still get the mileage credit for economy.

Dave