Given 10.5 hours I definitely recommend going into Tokyo. Your itinerary would look something like this:

8:00 - Flight arrives from BKK, go through inbound immigration and customs
9:10 - Hop on Skyliner train from NRT
10:05 - Arrive at Ueno Station

What you do for the next 4-5 hours is up to you, but options in the immediate area include Ueno Park (big park with art museums and a zoo), Ameyoko (crowded shopping street, lots of places to get lunch), Asakusa (about 5 minutes away on the subway, big temple, all the tourists go there) and Akihabara (about 5 minutes away by train, electronics/subculture district, all the tourists go there).

2:40 - Leave Ueno Station.
3:20 - Arrive at NRT, go through security and outbound immigration
4:30 - Flight leaves for ORD

The Skyliner train costs 2,400 yen each way. You can also take a slow train for about 1,000 yen each way, but I don't advise this because (a) you are likely to get packed in like a sardine during the morning rush hour and (b) it would take an extra 45 minutes or so each way.

Getting back to NRT two hours before your flight is perhaps good from a conservative perspective but it is almost guaranteed to leave you with more than an hour to kill at NRT. I would expect something like a 2-minute wait at security (which is generally very fast and easy in Japan, no shoe carnival here) and a 5 to 15-minute wait at outbound immigration. ANA tells people to get to NRT an hour before departure if they are already checked in.