My commute to the city is about 2.5 hours (90 minute drive, hour on the train) and I have done the spontaneous trip thing many times.
One Saturday morning last May, I asked my brother if he wanted to see RENT as a late birthday present, so I went on Ticketmaster and bought tickets for that evening's performance, and we left for the city around 3 PM.
Last spring, I used to do spontaneous trips to the city and go to TKTS. I always timed the commute so I would get there around 3 PM, when the booth opened for evening performances. I saw so many shows that way - Fiddler, Altar Boyz, RENT, La Cage - and I pinpoint that time period in my life as the beginning of my Broadway obsession.
I love spontaneous trips to the city! It's risky not planning anything - or planning last minute - but it's always exciting, rewarding, and worth every penny.
"The world is a better place because of hairspray." - Michael Ball