Variable Fatigue - This breaks all those step-functions (at skill+5 you
get -1 fatigue, fewer gestures, etc.) into a continuum which (I think) is more in the spirit of GURPS. I like these a lot.
Ley Lines - some ideas inspired by the mythology of the British Isles and described
in GURPS book "Places of Mystery".
Combat
Ranged Weapons ...
no defense (dodge, block, or parry). Cinematic and super
campaigns can do what they want, but for the 'realistic' (yeah
right, with magic and dragons, et. al) there is no defense...
'All-out-defense: erratic movement' gives -2 for the
archer/gunman to hit.
Perception -- use a full turn
('Concentrate') to see things beyond what is under your nose. This was a
good idea (from 3rd Ed. days), but it is hard to enforce.