If you're able to hit your spots and change speeds, you should be able to get folks out, though it's doubtful that those speeds will make you a "strike-out" pitcher. My advice for those who want to increase their velo is to seek out a quality pitching instructor and work on mechanics, core strength and shoulder excercises, and most importantly, throw the baseball. A good coach will work with you on a personal regimen that helps to strenthen your body, perfect your mechanics, and make you better at using your gifts to get folks out.
A good coach will be able to work with you to make you a better pitcher regardless of how well or hard you throw now. It's pretty difficult to do it on your own.
Good luck, and have fun!