All graduate programs have committees such as the "social committee" and "speaker series committees", as well as Graduate Student Organizations and other organizations to work on behalf of these programs. Is there any concrete career benefit to being an officer on one of these committees/organizations?
Those volunteer positions may help boost your chances of getting a major award. For example, one of the most prestigious graduate scholarships you can get in Canada is the Vanier Scholarship and the selection board uses your leadership experience as criteria for the award.
In addition to scholarships, it's always nice to have additional things to add to your CV to make you stand out. These skills can show a number of traits that employers may look for.
It's a bit of a mixed bag. While there is certainly a lot of benefit to performing service activities—you are giving back to your community, and that is both admirable and expected to advance at all levels of academia—you need to strike a balance. No activities at all makes you look too single-minded (can be a concern for employers). Too many activities and it will look like you're not committed enough to research (again a concern). You need to strike a balance between the two.
More than being useful on my resume, being part of a student organization in a leadership role gave me new perspective. It allowed me to exercise my mind in a different way and allowed me to hone my administrative skills, people skills and time management skills.
It actually had a positive impact on my research because I was more focused as a result of having a "lot more on my plate".
I am a firm believer that if it doesn't lead to a publication, than it is generally not worth the time of a grad student. In my mind the social committee is a no win time suck. The speaker series committee, on the other hand, is potentially worth it for networking opportunities. It might all you to interact a little bit more with speakers. Even mundane interactions (e.g., dealing with their receipts and reimbursement) is good networking.