I've been running a meetup for almost 10 years and I love it!
Attendance is usually about 70%-80%, I feel lots of love and appreciation for the work I put in, and it has led to several consulting jobs.
My key to doing it for close to 10 years is to do it on my terms. If I have other stuff that takes too much time, I don't arrange, if I have free time, I do arrange. No one can force me or push me to do it.
On average I host meetups 3 times per year, maybe 4, some years and I find that to be quite a nice sweet spot.
In terms of attendees I shoot for 30-60. I have done 100-130 people meetups, but that's too much work, so won't do that without personnel from the sponsor.
So yeah, meetups are fun but do it on your own terms only, and you'll enjoy it for a long time! =)