So far I have gotten radically faster by reading the sailing/racing books. Speed is certainly dependent on the skipper, as all the reading materials will agree with, however when you know how the wind affects different parts of your boat, and how to read sail telltails, bridle tell tails etc, in combination with practice practice practice, speed, skill and confidence will all go up. Phil Bermans' beginner book and Rick White's, Cat Sailing in the 90's have really helped my speed, by helping me decipher what is different on other boats that are pulling away from me and passing me. The differences are subtle. If you can't see other racers finishing, reading one book is not going to help you, but if you are charging downwind and/or upwind and you are plagued by your competitors creeping past you... a little book time won't hurt.
That being said... 100 dollar hobie tuning book sounds insane to me.
I have also learned a TON from just watching as much racing as I can.. Watching the America's Cup (back when they were fleet racing AC 45's) was VERY instructional because the coverage of the event was exceptional. On youtube for several of the events they have the same event with commentary for the masses, and commentary which is more technical.. Watching all of the tactics and strategy play out on the water, the jockeying for position at the line.. ect ect ect.. Just seeing what that looks like has really helped me a lot.. My time and distance estimating has gone from terrible to just needing a bit of fine tuning... and I have yet to enter a Regatta this year (even ones where I got my butt kicked after the gun, after even making A mark often at the front of the fleet.
) in which I wasn't able to nearly always be where I wanted when I wanted on the line.. And on top of that I have usually made the right choice about where to be...