possible, your blanket statement that bandits are a problem for everyone is not true. Personally, I've never had a problem with any bandits. You blanket statement about anyone who has ever volunteered or managed a race are also not true. I work about 40 races per year. Yes, that's FORTY. Not one of those races has ever had a problem or issue with bandits. Not one. Wonder why?
I have no idea what race you manage, but it seems like better planning might be able resolve many of the things you talked about. You know where problems develop, why not try to attack the problems before they start. Just some suggestions:
Your telling me you have enough bandits that they make your aid stations run out of water ?? You'd have to have more bandits than registered runners!! If that's the case, there's something else that makes people not pay to run your race. Are your entry fees outrageous ?? There's a reason why you have that many, I don't know enough about your race to know what it is. Maybe you do.
Concerning narrow stretches, it might be a course design issue. Maybe you're limited on where your course can go, but maybe it's possible to make changes that will eliminate those spots. People tend to spread out as the race lengthens, so maybe those spots can be later in the race ?? (If it's a loop course, maybe reverse the course?)
Chip timing would eliminate your results issues, but yes, it's a little more expensive than scoring it manually. Is it worth it to avoid the hassle of re-calculating the results ?? You have to answer that question. Most races with more than 500 runners can afford to pay for chip timing. If you can't, well ... maybe that's another management issue.
If your sponsors throw a fit with the way you handle things, then have them cough up enough money to change the way you do it. How bad is the PR your sponsor gets from a race that runs out of water, has results that are wrong, course is too narrow ??
Make your race WORTH running, and people will pay to run it. Bandits aren't your problem, they're the result of your problem.