I finally got around to ordering a brand new upper intake manifold, gaskets, and bolts. Found out Nissan changed the installation method by using shorter bolts and eliminating the metal spacer in each socket. It turns out over time the old (longer) bolts would stretch. I can confirm with the picture below:
Here are the shorter bolts Nissan is now using for the new intake manifolds:
So even with all new parts installed, no dice. Idle still surges after fully warming up, and I can still confirm the leak from spraying MAF cleaner underneath the intake manifold. My torque wrench is not very accurate, so even at 5 lbs I can barely get it to click. That's how I snapped the old bolt. I carefully hand tighten with the specific pattern, then slowly tighten each bolt. I even took it back out and tried to fully tighten one by one. No dice.
No shops were available to help me out, so hopefully one of my friends is coming by with a better torque wrench. After that I'm giving up. Engine runs great, but this idle surging with the intake manifold is PITA.
[EDIT] Took it to a friend's shop to check the bolts and install the oil cooler fan. He said the surge is so minor I shouldn't worry too much. This is in line what what Charles said as well. So I'll just move on and hopefully get it dyno tuned one day.