the ABS doesnt rely on the pressure or consistency of force applied to the pedal to "kick in". there are now pressure sensors taking measurements on the pedals!! - sorry G.
there are 3 speed sensors, one each on the front wheels, and a single one on the diff in the rear.
if your lights were off during normal driving, then generally your ABS system should be working ok, but you can test it the way vlade suggested. the codes for the ABS indicator lights are in the FSM. there could be other things wrong.
as for the ABS nervousness, i reckon its a personal thing, cos i'd feel far safer knowing that i can jump onto the brake pedal and electronic and mechanical controls will help me out to stop without sliding.
the "nervous" feel would be the feeling translated into the pedal from the constant opening and closing of the ABS systems valves. its a waaaay faster way of depressing and releasing the pedal to avoid the skidding tires!!!
also - i didnt know that the s13's here came out with 256mm discs. thought they were all the 280mm version. same diameter, slightly different thickness than the s14.
i always hear people saying the brakes on the s13 are crappy. i totally disagree, i've never had a problem with them. they stop me quickly, and accurately (without pulling side to side, or shuddering, or anything like that). but i do think its wise to do the simple s14/z32/r32 brake upgrade if you're going to increase power!!!