I'm president of our PTO this year, and here's what I've seen from being on both sides.
When you're not on the board, volunteering can seem intimidating, but honestly, these board members are just begging for help. ANY help. 5 executive members cannot run a PTA/PTO alone. They need and rely on volunteers to get any type of fundraiser, activity, event done and done well.
As easy as it is to judge these people for being standoffish or consumed, one must remember this is a volunteer position that they are doing in addition to working and/or caring for their own families. Most of the time if they're doing things with limited or no volunteer help, it's overwhelming. Try not to judge them until you've walked a mile in their shoes. I can't begin to tell you how many nights I've been up until 1am doing PTO stuff because I'm not willing to sacrifice my family time to do it. I don't need a pat on the back, but don't criticize me when their are a few bumps in the road during an event/meeting. I'm not a professional PTO person being paid to do this. I do this in my free time.
Most of the time board members do bond and become close because of the amount of time they spend together. That is normal.
Yes, there are PTO moms that are snobby, clique-ish and just downright nasty. See that before too many times. They are not the norm. Most want these positions to better their children's school, not to be "in charge".
We just did a "2 Hours Volunteer Challenge" at our school. We challenged each parent to volunteer just 2 hours of their time for this school year, and had a form to choose from. It ranged from one time events, to things that could be done daily, weekly, monthly. They range from taking a class to lunch, copying, library re-shelving, on and on...So far, we've had a great return on the forms and the commitments.
A Facebook page also helps when you need volunteers. People like to be "in the know". Start one and take lots of pictures to add to your posts. Parents love seeing their kids in pictures and respond well to that. Offer incentives that if you get parents to volunteer for an event, they get some type of prize - no uniform day, school water bottle, etc....
Good luck!