Certainly easy to do 2-3 days in each of San Fran, Chicago, Boston and DC.
Haven't really done much of Miami, but I wouldn't mind having a gig at those Art Deco buildings.
There are plenty of city tours in both San Fran and Chicago. There are just so many things to do in San Fran (Union Square, cable cars, Haight-Ashbury, SoMa, Embarcadero, North Beach, Fisherman's Wharf, Painted Ladies, Castro district, Golden Gate, Coit Tower, Lombard St) that it's hard to do them all except on a tour. Those tours usually stop at each spot.
Chicago too...usually start from Grant Park...try to do an evening cruise out onto Lake Michigan...the evening skyline is quite spectacular. And the architecture of the buildings along the Chicago River. Wrigley Field, Magnificent Mile, Water Tower, Art Institute (one art gallery worth going to - Nighthawks, American Gothic, Dorian Grey, lots of Picassos).
Boston has all the historic areas...there's a straightforward walking tour. Plus Faneuil Hall and Quincy Market. And Fenway Park if you're that way inclined. Boston Common and Beacon St (Cheers bar is on Beacon St IIRC)
And DC - you've got to allow a couple of days for various Smithsonian buildings - I concentrate on the 19th-20th century stuff like the Air Space one, the first US computer (ENIAC ?). Another day can cover Capitol, White House, Ford's Theater, Lincoln Memorial, Washington Monument, The Reflecxting Pool etc, Arlington.