Another interesting tidbit about Gramercy Park (the park itself, not the neighborhood) is that it is the only private park remaining in New York City. You have to be a resident of an apartment that faces the park to be given a key to the big iron gates. As a result, the apartments have become prized real estate, even though the park is quite small by NYC park standards (excluding the "pocket parks"), and (in my experience) you hardly see anyone using it, even in the summer.
If after admiring his statue you're interested in Edwin Booth, there is an excellent play (called "Booth") about his relationship with his father, Junius Booth. Junius, after he emigrated from England in 1921, was considered to be the finest actor on the American stage in the middle of the nineteenth century. Edwin went on to surpass his father's theatrical fame, in part by shifting the theatrical focus from his father's "Richard III" to concentrate on a more emotional, introspective "Hamlet"; previous to this Richard had been considered the greatest role in Shakespeare acting. Even John Wilkes had a prominent theatrical career before he committed his most famous act.
If you find yourself by Grammercy Park, though, the first thing you should do is go to the south end, walk down Irving Place a couple of blocks and have a beer at Pete's Tavern, which has been there since 1864, making it one of NYC's oldest.