I totally sympathise so what I do is this:
1. If someone (kid, adult whoever) is talking, messing around or being generally annoying I ask them to stop once, then if they carry on I complain to an usher. If that doesn't work I ask for the duty manager and complain again. That usually gets them chucked out/hushed up and/or my money back.
2. If nobody on-site doesn't act on my complaint I get in touch with head office and complain to them as soon as possible telling them what happened - include date, time of screening, brief summary of events, and include names of ineffective staff if possible etc. More often than not you'll get some sort of compensation (tickets, monthly passes, free food etc) and you'll see a very different attitude the next time you visit that cinema - it's amazing what a kick up the arse from head office can do to sloppy staff!
Dirty toilets etc - complain and mention Environmental Health. Next time you use them they will probably be so clean you'd be able to eat your dinner of them (not that I'm suggesting you should or would want to of course..)
RE: The popcorn thing - it's true. The cost of the popcorn itself is so minor that it does indeed cost more for the buckets than the food itself. For cinemas, the food stand is effectively a licence to print money!
I've seen this from both sides - as a customer and having worked in a cinema for 3 years as a student. Oh, the stories I could tell you .. happy days!