Yeah, but if you lost 20 lbs AND spent the $1000 on lightweight parts, just think how much faster it will be!!
But seriously, if you can lose some weight as a driver and still end up modding for weight reduction you're just that much farther ahead. Every little bit counts. I have the build of a horse jockey so it isn't even an option for me. If I lost 20 lbs I'd probably look emaciated.