The best thing about NBA Street Vol. 2, the primary advantage it has over the first game (to me anyway) is the inclusion of all the NBA legends. It was great seeing players like Magic Johnson, Wilt Chamberlain, Larry Bird, Bill Walton, and Isiah Thomas. I also liked the handful of ABA legends; Julius Erving, George Gervin, David Thompson, Moses Malone...
As for NBA Street Vol. 3, if I had my way I'd just have them add everyone on the list of the 50 Greatest NBA Players (they voted on it about 6 years ago...check the History section at nba.com) but since space probably doesn't allow that I'll just choose my favorites:
Kareem Abdul-Jabbar (why WASN'T he in Vol. 2???!?)
John Havlicek
Bill Laimbeer (no jokes about Combat Basketball please ^_^)
Hakeem Olajuwon
Dolph Schayes
Kevin McHale
Charles Barkley
Willis Reed
Patrick Ewing
George Mikan (that'd be interesting)
Robert Parish
Dan Issel (just for more ABA representation ^^)