I'm currently in school to become an RVT/LVT, and plan on continuing on to do vet prereqs and vet school in the future.
I can agree that you certainly don't have to have it to get the experience you need to apply to vet school, and that it will in fact put you behind because typically the science courses required for the RVT are specifically geared toward that program, meaning that they will take up time you could be spending on prereqs like general bio, physics, chem, etc.
BUT...
Becoming an RVT/LVT can have advantages. For example, if you are at all unsure of your desire to be in veterinary medicine, the classes will certainly help you figure out if it's right for you. (Or, if you are like me, they can "fan the flame" and make your desire to go to vet school twice as strong... lol) Being an RVT also means that you not only learn, for example, how to run a blood chemistry, but what those numbers mean. Which I'm sure could be very useful in vet school, knowing that you already have a pretty solid general knowledge of things that many people have to start from square one on. Not to mention being registered, as others have said, boosts your resume and opens up more job opportunities. Oh... and, one of my favorite advantages... most of the professors for our vet tech program are also vets, which means that when I do send in my vet school apps, I can have recommendation letters from people who can attest to both my academic abilities AND my clinical skills/knowledge of the field/etc---all in one letter!
Not saying that you should or shouldn't do the RVT thing. Sometimes I wish I hadn't because I could almost be done w/ pre-reqs by now (if not completely done), but other times I think about how much I'm learning, and the confidence I'm gaining in my skills, and I feel a little relief knowing that it may give me just a slight little edge in the battle w/ the mountain of textbooks I'll be facing when I finally get into vet school.
Either way, good luck!