Scientific and technical writing is a little different from the kind of "creative writing" you are taught at school. There are different conventions. For example, "vary your vocabulary" is a complete no-no if you are striving for precision and lack of ambiguity. If you think using the same word several times may sound a bit clunky, and you decide to make things "read better" by using synonyms instead, imagine the internal dialogue of your readers going something like this: "You talk about a thingumabob here, a thingamajig there, and a whatchamacallit in your other paper. What subtle distinction are you trying to make? I've been trying to puzzle this out for ages. Oh, I see. You are just varying your vocabulary. Come here and say hello to this two-by-four." That should help you decide not to do it.
One important part of a scientific paper is the abstract. It should be short yet comprehensive. It should tell you what the paper is about, the question the paper addresses, and the answer it discovers. It is not a spoiler to put the answer in. You are not writing a blurb for a whodunnit. Don't worry that you are giving away the punchline. The abstract may be the only part of your paper the reader even sees.
So I was delighted to see a paper with an excellent abstract quoted at Ben Goldacre's secondary blog. (Actually, it's only the perfect abstract when combined with the paper's title; techincally, abstracts should be stand-alone. But, hey.)