but but teh blue shells mean anyone can win! So does the smash ball in brawl. Damn casuals.
But yeah, as has been pointed out many times, the only thing that provides a distinct disadvantage to first player is a blue shell. Lightning effects the earlier players only slightly more than the later ones, pow effects everyone ahead of the user equally (ie not at all, in some cases it actually speeds you up cos you can cut corners over bad terrain). The items are not overly bad. First gets lots of protection items, 2nd gets lots of red and green shells, but has to watch out for 3rd who gets similar. All the good items only occur if you're 7th or worse, and then you're likely to get hit by a bullet from behind so it's not a great position
Also a good example of how it takes skill to win. Every time a hacker spawns infinite blue shells, I end up winning! Just gotta be cheap and sit close behind him with mushrooms/bullet/whatever - the hackers are never any good