I think speech & debate is like a lot of other EC’s in that it depends what you do with it. Lots of kids list “debate club” as an EC when all they do is attend meetings and hardly ever compete. My D is a senior who was accepted ED1 to Pomona, so she withdrew her other apps and we don’t know what would’ve happened with them. But she was able to list a lot of accomplishments, including being a finalist at many competitions, qualifying for Nationals twice, qualifying for TOC, reaching the highest level of the NSDA honor society, getting the NSDA Academic All American Award, etc. So there is an opportunity to demonstrate achievements at the state, regional and national level. Also these accomplishments are easy to objectively verify if an adcom were inclined to check. On the other hand, I certainly wouldn’t recommend it for a kid who doesn’t enjoy it. For my D, she has enjoyed every minute of it (and will be competing all through Spring semester even though she was accepted to college in December) and has learned a tremendous amount from it.
Is it “enough” by itself to get someone into a highly selective college? I’m sure the answer to that is no. The rest of the package, GPA, test scores, essays, rec letters, etc are obviously critical. My D also had two other EC’s that together with speech & debate made up most of her EC’s, but speech & debate was the big one. I’ve also seen kids who spend so much energy on speech & debate that they let their GPA suffer, and I would definitely not recommend that!
Here’s a link to info on the value of debate: http://hwdebate.org/the-value-of-debate/. That particular site emphasizes debate but speech is also a great activity. A lot of kids love theater but don’t have the opportunity to win awards that they can list on their college applications. Doing speech events like dramatic interp, humorous interp, duo acting, etc is a great way to express oneself theatrically while also getting awards.
Our school’s speech & debate team has a pretty good track record of kids getting into great schools in the last 3 years (the ones I know about), including Harvard, Stanford, Columbia, Duke, Pomona, Claremont McKenna, Wellesley, Tufts, West Point, Vanderbilt, GW, American, etc. And this is at a public high school.