How does the performance of a warped pan compare to a level one when using gas? Of course there will be hot spots when using it on anything besides gas because it won't sit flat.  But are there any performance disadvantages when using a slightly warped pan and gas? As far as I can tell even a brand new pan will still pool oil depending on how level your stove / floor is.
A slightly warped pan will perform the same as a flat pan on gas from an efficiency perspective, the shape isn't going to waste energy. As for whether the warp will impact your cooking experience it's hard to say, a warp can cause coatings to flake off, or make liquids pool in or run away from particular spots.