Hello Ken
First of all it is important that a full check is carried out by your vet just to clear any physical problems.
Regarding the "odd behaviour which appears to by cyclical", we would need to know if this is only the second time this has happened or has it really occurred every 6 months since you have had your dog. If there is no underlying medical reason does the behaviour occur when there is some external factor e.g. fireworks (autumn) and wind and thunderstorms (spring) which makes the dog fearful of going outside unless both owners are there for security?
Regarding the excitement in the car, this could be excitement/anxiety or controlling behaviour - excitement as the walk always ends in something exciting, anxiety - he could actually be fearful of the car and is seeking security in the front with you or he could generally be quite indignant about being restrained in the back - especially if this is the only time he is restrained.
If this is excitement and not fear/control issues then when you get him out of the car you could do some 'boring' training to take the edge off his excitement. Additionally you could take him on car journeys that don't end in a walk.
Although you say, in the last week, no negative incident has occured, there may be something that has gone undetected or a gradual build up to this problem that has gone unnoticed.
Your wife going out every 5 - 10 minutes before he goes to sleep, it might be better not supporting this behaviour and instead of trying to take him out take him back in and ignore him. Otherwise this behaviour can quite quickly turn into attention seeking behaviour.
Ken, it is not clear from your post what the underlying cause may be. This is really the type of case that needs a home visit - it is then much easier to assess the relationship the dog has with its owners and therefore establish the likely cause and best way to resolve it. It would also help to see the dog's general demeanour. We would need to know how he behaves around the home, is he afraid of anything, is he an obedient dog, does his behaviour change in any other way etc etc. Also to help motivate him we need to know what he likes doing - is he a good eater, does he like to play etc.
Whatever the reason it is important not to force the dog into the car or out on walks as it will result in deterioration of the dog's behaviour.
Hope this can form a basis for a reply but do let me know if you need any more details or if I can be of any further help.