New Dehli, India Airport layover

I was in New Delhi for a few days after first arriving there in Summer during the monsoon rains.
Be cautious regarding the time you have, as the traffic can cause massive delays and if you're going during monsoon season roads can close for hours due to flooding without advance notice.
With that being said, please bear in mind that

a. I was last in India about 12 years ago, so things may have become more efficient,
b. I had a really wonderful time while I lived there, if you can find more time to go there are endless things to see

Honestly, you're better off finding somewhere within the airport to hunker down. The city of Delhi is about an hour away in normal traffic- never mind during periods of congestion ... which frankly is most of the time.
Add the particularly tight and sometimes time consuming security measures getting back inside the terminal once you've left and you have the makings of a very stressful experience indeed.

Are you connecting to go to another Indian city or to another country (Nepal, SE Asia, etc.)? Americans need a visa to enter India so, if you are not getting a visa anyway for further travels in India, it’s probably not worth the hassle and expense for a few hours.

I have flown through the New Delhi airport on my way from southern India to Nepal. What I remember is that it is quite large and sprawling. I don’t know how far the airport is to any location that a tourist might want to visit. Traffic and security could be a major concern. I don’t think I would risk it.

Also, will you be coming off a really long flight? I have traveled multiple times to China, Singapore, Thailand, India, Nepal, Uzbekistan, South Korea - and those LONG flights leave me with little energy for sightseeing right away. A shower, a nap, and a meal are what I want upon arrival! I would suggest you check out options within the airport. There may be a hotel inside the terminal or maybe you can buy a pass to a lounge.

India can be quite overwhelming to a first-time visitor with its sights, sounds, smells, but it is amazing. I took a tour in the south that was a highlight of my many travels. I hope to return to see more of the sub-continent in the future. But a few hours just to say I’ve “been” there - uh, no.

If you do decide to stay within the terminal you might research the Plaza Premium Lounge - which offers shower facilities and nap rooms for up to about 5 or 6 hours if you'd like to freshen up and feel a little more human before proceeding on to your final destination. Would make for a much more pleasant layover than gutting it out going to one duty free shop after another.
As I recall the cost for a 3 or 6 hour block of time is really quite reasonable.

I am thrilled with all of the replies. Yes, we are on our way to Singapore, and my 1st trip to Asia. It looks like we might need to enjoy the terminals(s), take a shower and clean up to avoid and additional stressors and wait for our our next flight. (wow, 8 and half hours)