Let me explain it by my own experience: polishing the exhaust ports makes me loose high-end torque but gives me a little more low-end torque. And overall I even loose torque :D. In my case this is bad with my little "1.6L" blacktop so I had to buy and install a complete 'new' cylinder-head witch cost me over $300! But hey if you like low-end torque then shoot go ahead polish the ports...:hmm:
If you really want to fine tune your car or any car, after every modification take it for a test-drive or dyno-run...Not every modification is needed and so not every mod comes in you advantage