Yes you can squeeze more out of them after you do some upgrading. But those parts wouldn't have been on a stock setup so unless Nissan was going to set the stock performance bar higher they wouldn't have done any good.
1989 240SX Fastback. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1995 300ZX Twin Turbo Warning: Objects in mirror aren't as fast as they thought they were.