@TS:
IMHO playing Guitar Hero wont improve your actual playing..
but others will say it will practice your picking hand well, ryhthm and timing
Playing Drum Hero, IMO will somehow allows you to practice some drum rolls, as
well as the rhythm and timing..
Playing Rockband as whole, was designed for entertainment, familiarizing with
different music styles and artists..
In Conlusion:
To improve your actual playing skills practice with a true instrument..