When I check the plugs for mid throttle air/fuel ratios... can I just rev the RPMS up to 3000 for a minute or two in "Park".. or do I actually have to drive the car @3000 and immediately shut it off and coast to a stop?

Thats the way I used to check jetting but it was at WOT and cut clean and coast. If its not a race car , I would just try to do your driving and bring in an park it, pull plugs when it cools down. After a couple of reads , you should be close to telling you what you need to know. I wouldnt do this in park or in an unloaded engine.

You really need to drive it and place a load onto it. By doing it in the driveway with no load, you don't use the circuits you're looking to tune. You're not using fuel from the main fuel circuit, throttle isn't open enough.

Use a vacuum gauge and run it into the interior, you'll see the difference between the driveway and the road.

Intermediate throttle is generally considered an open throttle drawing 10 in./Hg of vacuum. Idle will be 18-20 in./Hg, with a stock cam, and WOT will be 0-1 in./Hg.

Always remember where you came from, t will be important, take notes.

You really need to drive it and place a load onto it.
or do I actually have to drive the car @3000 and immediately shut it off and coast to a stop?
Yes...and that is what a dyno does
For road testing mixtures and dont have a dyno, a portable gas anayliser on the lap of the passenger in the car is the best bet.

Your best bet failling the above is drive around normal for a few days, then find a good long hill, load the engine then shut down before the load comes off and coast to a stop.

A caution thu...do not run for a few days then pull on the highway and open it up...this will not clean the plugs but the higher temps will glaze the deposts on the plugs giving a faulse reading.
Ever noticed on a trip, after about 50 or 100 miles the car seems to perform/sing? This is the piont at which the glazing finally burns off.
To bring this piont down to low milage, pull on the highway, and gently increase speed ove 4 or 5 miles to around 70 mph, then drive normal...this burns off desposits without glazing them to the plugs.