That is similar to what I said a while back about my 1310 cc Cooper 'S' rally car. With its history of 32 historic rallies and 5 outright wins it is worth quite a lot. It is/was a well-known car and has been featured in both of the 'comics'.
So what would I do if I comprehensively damaged it on an event where it was not covered by insurance?. Would I just scrap it and sell off the bits which were still OK? Or would I use a used and restored Mk.1 shell and re-build the 'S' into it with everything built exactly as before the crash?
I will leave you all to guess 
. It's easy to be 'holier than thou' when it can never be an issue for you, but in the real world things are different. Whilst many of us do enjoy competing in motor-sport, we can't just afford to scrap a £40k classic car and when a simple solution is available who would not do exactly that. To think otherwise is, quite simply, naive.
To answer the above from MIGLIACARS, I think I might just build a 970 'S' rally car and use it on historic rallies or let my son and grandson use and enjoy it. With some class wins at international level it would generate its own value.
By the way, it's not only with Minis that this happens. I know a lot of members of the Sunbeam Tiger O.C. both here and in the USA. Now Sunbeam Tigers do rust, just like Minis and many owners have used Sunbeam Alpine shells in order to keep the Tiger in existence. Tiger shells are slightly different, but with some careful modification they are almost identical. In this country the Tiger O.C. accepts this as necessary, but in California these 'hybrids' are not so well regarded although they are beginning to realise that unless this is done the numbers will simply decline. My son is currently building a 1978 Ford Escort RS2000. As a base he has a 1978 Escort 1.3 2-door and we have modified the body-shell to full Escort RS specification. Once done it will be absolutely identical to a 'genuine' RS2000 and will be accepted in competition as such. Other competitors have no issues with this and the car will be worth a lot of money when completed with c.175 bhp. I am looking forward to driving it later this year.
It is certainly the same with Cortinas and I know of a Vauxhall VX4/90 which started life as a Victor 1600 Super, but is now a full works rally replica.
The Federation of Historic Vehicles has been lobbying the Gov't to allow re-shells where this saves a classic car.
On the subject of illegality, speeding is also illegal as are lots of other things, so let's not become paranoid about which laws we like and which we don't, then have a go at those who don't have the same points of view.
