Revalving the fork and rear shock were the single best improvements made on my 640 Adventure.
Everthing about the bike felt better - cornering, bottoming, whoops, even riding straight down the highways.
IMHO respringing and revalving forks should be the first thing done to any bike - even before pipes and stuff. It makes that much of an improvement.
you would probably be a much smoother and faster rider with good suspension rather than any engine work you could do.