The HP comes from bumping the timing (which requires higher octane fuel) and adjusting the A/F a little (which is best done with a dyno with A/F readout).
So if you are looking for power gains, don't get a programmer. However, like the others said, you can make your auto shift firmer, change shift points, change speedo (if you get gears), turn off MILs, etc.
It might be worth getting after you get all those mods put on your car and getting a custom tune.