Hi Jewel - First of all, I bet I'd love your group (not that my loving your group would get you a heck of a lot

). I don't think we're far off.
And yes, I do think there's a distinction between volunteers and "just parents". In fact, I usually use a 4-level ladder.
At the bottom are the folks who aren't connected at all (yet)
The next level are folks who attend school events
Next is worker bees
And top is the completely insane people (like most reading here) who get really into this stuff and give a ton of time (and the dining room table), etc.
The top doesn't want to be served. Typically, your worker bees have also been drinking the Kool-Aid to a degree (though these are the folks for whom your "pleasant" description really applies) and are probably doing the serving. But those last two levels need fun. If you want those who never attend to attend -- then your events need to be good and, yes, fun. And if you want those who attend now and then to maybe move up and help once in a while -- then their experience in attending should be fun (else they'll have little desire to move up).
That's my take.
By the way, I'm not talking about you juggling or doing magic tricks or telling great jokes -- when I'm talking fun. (Though by all means -- if you can... juggle away!). It's more of a spirit and a lightness and a distinct lack of any hint of guilt ("you should do more for the children"). Those things matter.
Tim