A ported throttle body is intended to optimize air flow and promote air velocity which will provide benefits on any engine, but if the throttle body is too small, it will still be a choke point.

Are ported throttle bodies worth it?

Yup, throttle response alone is worth it. Most people claim a few horsepower gain, but you'll realistically never feel it, even with a finely-tuned butt dyno. The ported throttle body reduces the time between your foot rolling into the throttle and the engine actually going, noticeably so.

How much horsepower does a ported throttle body add?

Gains from a throttle body can be dependent on modifications. Generally speaking, anytime a throttle body is added, there will be some added horsepower. The amounts can range from 5-25 HP depending on what other modifications are done to the engine.