Nah, I'm not implying that admission committees would select an inferior first time applicant over a superior second time applicant. But if they comparing two very similar applicants (which, let's be honest, they almost always are) and one is a reapplicant that has not shown a significant improvement from his/her last cycle, then I think the point goes to the first time applicant.
In response to the usefulness of writing a PS/secondaries and attending interviews, I'm sure that would help in some regard, but to what extent? Enough to outweigh the reapplicant disadvantage? Maybe, maybe not.
Want to write a PS? Go ahead and write it. Have it critiqued, you should have ample time to perfect it during a gap year.
Want to write secondaries? Head over to the school specific forums on this site to get the secondary prompts and go nuts.
Want interview experience? That's what mock interviews are for. Do as many as you want, YOU'LL HAVE AN ENTIRE YEAR.
To be clear, I have no idea how prevalent this "reapplicant disadvantage" actually is, I'm only saying you should be wary of throwing your application in the ring just for the hell of it. That said, there are absolutely certain people who should just go ahead and apply.