As long as you have the energy to do it or the volunteers to head it up, I say go for it. I think that you'll know (based on attendance and enthusiasm) when you need to back off. I'd love to do a family night once a month and I think that its a great jumping off point to get new volunteers. People don't know what PTO is about until they see you in action then most of them can't help but get involved.
If I've learned anything from this site it's that you have to let parents know what you're doing and why you're doing it. Family nights will eventually equal big bucks from fundraisers and many volunteers.
This year our PTO has been pretty uninvolved. We've had one movie night that no one wanted to volunteer for but ended up being a huge success. Our holiday party has all of 40 people (that's people, not families) attend and our fund raisers were disappointing at best. The old board will be moving on next year and myself and one other mom are excited about starting fresh next year. I have a ton of ideas and could easily do a family night or event every month but I wonder if that is too much. What do you guys think?