Honestly, dude, those air gaps look normal, assuming the throttle lever is touching your idle speed screw. You have to have them open at least a little bit for the car to run. Is that photo with your primary throttle plates COMPLETELY closed, as in, no idle speed screw limiting their travel? If so, then yes, that's too much gap - send it out to get fixed by a pro.
You may have to have your throttle plates rebushed, and honestly, like I said, I'd send the throttle plate out for that service to Cliff or maybe Mike at QuadrajetPower. If you mess it up, it's game over. It's common for quadrajets to have worn primary throttle shafts, which allows for air leaks. Secondary throttle shafts don't need to be rebushed, especially since it's important that they aren't "too tight" as to allow the large secondary butterflies to properly close. Spray some carb cleaner in those areas while the car is running and see if it changes your idle. Did you spray all around the intake to see if it causes a fluctuation in idle? Also, try opening the secondary air valves while at idle and see if that makes a change - and by air valve, I mean the ones at the top you can actually see and are opened by vacuum. While at idle speed, if you manually push down the secondary air valves, it shouldn't make any difference in idle since the secondaries should be fully closed tight. If there is a change in idle speed, then the issue is with your secondary throttle plates not fully seating closed.
Also, what emissions equipment are you using? If all your emissions crap is still hooked up and your car is running hot, there is a very remote possibility that your DS-TVS is adding timing to your idle like it's designed to do when the sensor detects a coolant temp of around 205+. By adding timing, it speeds up the idle, therefore water pump circulation - plus, more timing at idle typically makes the car run cooler. This is very unlikely and would only make sense if you're running hot while the idle is high, and you have all your emissions equipment hooked up.
Finally, what tension springs do you have in your distributor? If you have those crapola "light" springs (usually copper in color) out of those recurve kits, it's possible that you're adding timing at idle that you shouldn't be adding. Stock distributor springs are usually very heavy and stiff as to prevent this - as in, when you rev up the engine and return to idle, it returns to where it should. If the springs are too light, you'll create a positive feedback loop that ends up raising your idle speed once you rev up the motor. The point of those light springs is to have your mechanical advance come in early for performance, but they're not very practical for street-driven cars. The ONLY timing that should be present at idle is your base timing setting (which for your W72 should be 18 degrees BTDC), which is set WITHOUT VACUUM ADVANCE, and then your vacuum advance on top of that if you're using manifold vacuum. And you need a timing light to correctly set timing.
One more thing - the only reason you're making that healthy 20 or so inches of vacuum at idle is BECAUSE you're idling so high. Once you get your idle down to a reasonable level, you'll probably end up seeing 16-17" on the vac gauge, which is still perfectly healthy.
