I think if you send the same release through 15 different wire services, then that could trigger things (People could consider it like a spam, or like an irrelevant content...) That's why i think you must try to diversify the PR by writing different versions of it on the web and be really selective on the news wire services (Which are the best for the topic of your release? Which are the ones that rank well. etc.).

Any thoughts about that??

I think that's good point you made! Also, Google leaves out search results if they are too similar, so your press release won't be seen as well on the results as you hoped.
Of course you click on show all results, but search engine users wouldn't really bother with that.

If you just write a few versions of the press release, wording the title and first paragraph a bit differently, you don't have this problem.