Racial illusions don't grant any racial skills, elemental resistance bonuses, or experience bonuses (or in the case of the big dumb fatties, xp penalties
[You must be logged in to view images. Log in or Register.]). As mentioned above, the main benefit of changing your appearance is to affect your faction. Additionally, becoming a dark elf grants ultravision, and changing into a troll will give +1 HP regeneration per tick. Unfortunately, the infinitely cooler looking Iksar illusion doesn't enhance your regeneration. Because of a graphical bug, transforming into a gnome will allow you to see thru some walls if you stick your nose into them. Heck yeah x-ray vision!