The other mistake I think you made was to go into the event with only one goal in mind. Once it become clear that you weren't going to achieve the goal, you got demotivated to the extent of stopping. So much of marathon running is mental; keeping yourself going when you know you're not going to achieve what you set out to that day is often harder than pushing through physical discomfort. Try having an 'A', 'B' and 'C' goal next time - the 'A' goal is what you want to achieve if everything goes to plan, the 'B' goal what can be achieved if everything doesn't go to plan and the 'C' just to finish, assuming no broken bones or serious injury.
All things considered, it ran relatively smoothly for a first time event. There's things to be improved on for next year, but hopefully being able to use the original course will help there and perhaps the council will be more accommodating, as there's clearly demand for such an event in the local area. I did find it surprising that some people said they were wrongly directed at the fork for the finish/start of the third mini-loop - surely you know roughly what distance you've done and whether you're due to finish or not? Mind you, I also saw someone heading the wrong way around Admiral's Park and trying to re-route someone going the right way, so who knows?
That's a brilliant idea. Maybe these people who are so keen to inflict their musical choices on others should be forced to become pacers and have an annoying jingle on a loop for the entire event. Something along the lines of "I'm the 4-hour pacer" to the tune of "10 Green Bottles".