I agree. I just used one personal statement for my application, with a small paragraph about the importance of a solid foundation in internal medicine. If I'd had more time I probably would have written a separate one for prelim programs (but if I'd had even more time, I'd have written a separate application for everywhere I applied. At some point it becomes logistically impossible to do all of this).
BTW - I used a 'service' to help me write my LOR's, and hadn't completely decided between IM and Neuro, so I received an LOR for both. They were almost exactly the same. The only thing that changes is why you decided to go into the field, what draws you to the field, and where you see yourself in 10 years. Your other basic information is still going to be the same.
I think you'd gain a few points for writing a prelim essay and a separate neuro essay, but it's not going to make or break you by any means.