It's funny, I am about to meet with our volunteer coordinator on this exact issue! I do think you have to listen to your audience who don't want to commit to anything at the start of the school year. We're changing our approach too, we used to send out forms on the second day of school so people could sign up for jobs, but who can really commit to something in August for the next April? And it's not a great place from which to start a new school year. Many people balk at PTA in general when they feel like they are always being asked for money or jobs. Rebrand your breakfast as a community event, a Back To School social to just visit and get to know people. Don't hard sell volunteering, just be great representatives of the organization -- mingle and be good hosts, introduce yourselves around and be friendly, introduce people to those who might work well together (so-and-so is really crafty, introduce her to the Event Chair who needs raffle baskets put together). I tend to think that the best recruiting happens organically, between individuals in person, when there is something specific to speak of. It's much easier to grab someone at drop-off and say "can you help Susan for an hour hang decorations" rather than, "will you join the decoration committee for next February".
But also make the volunteer information available to people. We post job descriptions on our school web site, along with specific urgent needs on our PTA bulletin board near the office and in our weekly online newsletter. You could put together an information packet or a poster to display at the breakfast, which gives an overview of the ways people volunteer at your school, how much time is involved, and whether it can be done at home. Then let that speak for itself, and let the breakfast be social.