my 2p,s worth...for what its worth
If you have built a car that can take the punishment that a track car will no doubt be given ( enjoying yourself
) then for the extra expense of making that said car road legal will be worth it the first time you go for a "drive out" with a few other 7 style cars,
better than riding as a passenger in someone else,s car or not getting the chance to go at all
Nothing to stop you making it into a track car for say the summer months then upgrade it over winter to make it IVA ready/pass the IVA, & then the following summer you can do either...track or road whenever you wish.
this way you can build the car, enjoy it on track then upgrade it, which also spreads the cost over a period of time whilst you still get to enjoy the car
cheers
andy