I'm sorry but I can't comprehend how you don't see the difference between 30 and 60 frames per second. If you really can't, good for you, you require less than I. I know for a fact:
People with higher FPS in SA-MP move faster
People with higher FPS in certain CoD4 maps can get to areas others cannot, and past 200 or so they have no footstep sounds.
There are other examples, but this is enough to show that higher fps should definitely be striven for while lower fps should be frowned upon, and that it definitely does make a difference.