I finally got a chance to poke around through Grand Central Madison and it rely is beautiful. I'm a fast walker so it didn't seem like too long of a walk, but if I needed it regularly I'd need to find the quickest route.
It did seem like a ghost town. Very few customers going in or out, but MTAPD was posted everywhere which was nice. It was off peak, but even when I walked into MNRR area, it was so much busier (and I do realize how many more trains there are for MNRR than LIRR, but still)
I think there was also an Iphone launch or something bc the apple store had a huge line