My main target at the moment is a May marathon, but I have a half booked in 2 weeks time that I also want to race and get a PB, I've been right up for this until reading this thread and now how doubts as to if I should or not. So many people say a good half a few weeks out is great, but you make valid points about recovery effecting the rest of your training for the main goal...
Enter a race. I'm a very lazy runner and totally agree with you in this cold miserable weather I can easily find a reason not to go for a run (can also find reasons in lovely warm weather as well, I'm just that lazy), so I enter a lot of events every year keeps me motivated enough to get out the door on even the most miserable days. And once I'm out I'm happy, doesn't take long to get into your run and wonder why you ever thought of putting it off.
I have been out for a run before and my planned route has taken me along a section of an event that was going on (I didn't know about it till I was there amongst loads of runners) one of the marshals did get a bit arsy but didn't actually stop me. I was only on the route for less than 1\2 mile though till I had a way to change my route and get off their route.
Guess there is nothing stopping anyone following the whole route if on public highways. Although if there are road closures would the road still be in public access? As no regular users would be able to access it in the normal way, so that must be a grey area at the very least.