Conventional wisdom would say that it is not the "volunteering" that is important, rather it is:
1. Showing the drive and ambition to get involved in something that interests you
2. Having the leadership ability to make an impact in that activity
3. Having that interest tie to your story
4. Extra credit would be to have that activity be something that the school could benefit from (like a musical talent) or that differentiates you from other applicants.
I'm in the same boat: I travel M-T for work, which makes it difficult to get involved in most activities. I've seen people without significant "extracurriculars" get into top schools, and I've seen people not get in. Without a gigantic database of applicants, there really isn't a scientific way to go about identifying the incremental impact of it on an application (on top of every other variable + luck).