mate
in all the time I have known you I know of the camper being used once.. that was to drive to the MOT station and back
you obviously love the track events and want to get into it a lot more... and the camper isn't getting the love it should have otherwise you'd have been tinkering with it a lot more, and as you said it needs work doing to it - i can see it turning into a shed
getting a car fully prepped for the track will be an achievement, you'll have an end goal and then when you are racing you can aim higher and higher
i'd say opt for the track car, will keep you focused and also give you a nice excuse for father/son bonding