Based on my own experience, I would definitely recommend applying for the travel grant!
The pros you have mentioned are fairly substantial. Regarding the con: I have never found any conference volunteer job to be at all onerous*, and usually they have been fun and/or valuable.
For example, here are some volunteer jobs I have had:
Volunteering at the registration desk
If I have this job, I get to meet all the attendees as they come in. Usually, when I first sit down at the registration table, I flip through the badges to see who is registered, and make a plan for who I want to meet. Then, if those people come in while I am "on duty" and they are not in a rush, I can strike up a conversation.
By doing this, I've been able to have some really "spontaneous" talks with important people in my field who I wouldn't have had much of an opening to meet otherwise.
I've never been asked to do this job for more than a couple of hours at any given conference, so I didn't feel like I was missing out. If this is my volunteer job, I can usually arrange with the other volunteers so I am "on duty" during a time when there are no sessions I'm interested in anyways.
Taking minutes in meetings
Another time, I was a student volunteer at a conference that also hosts its sponsoring SIG's annual business meeting, and my job was to take minutes in this meeting. I got to listen in while all the big shots in the SIG talked about what they really think of the state of the subfield, the quality of the conference, the direction they'd like to see things go in, etc.
Also, the meeting was in the evening and there were no conference sessions going on, so I didn't miss anything while doing this (except maybe a nap).
Mic shuttler, running the 1-minute madness session
Some volunteer jobs take place inside the conference sessions themselves, so you don't miss out on anything while doing these jobs.
For example, I've been assigned to be the person that carries the mic around to people who have questions during the Q&A after each talk.
I've also been part of keeping the 1-minute madness session (where poster/demo presenters get up one after another and speak for one minute about their poster) on time. The student volunteer coordinator described this job as follows:
1 person in charge of lining up presenters in the correct order, 1 person in charge of advancing the presentations, and about 5 are responsible for throwing the presenter with crumpled paper balls at the 56th second to get her/him off the stage.
(I didn't have to throw any paper balls.)
* YMMV. At a large, well-organized conference there will be lots of volunteers, you can choose which task you prefer, and no one student has to do too much work. At a smaller conference, things may be different.