The majority of historic rally cars are built from standard road cars. 'Restored' competition cars are generally ex-works jobs that will cost you more than a brand new Lamborghini. Or two....
I'd still happily 'ruin it', as I'd prefer to see it actually out competing in a rally, race or hillclimb than sat on a field in a 'classic car show' which bore me to tears.... My son, three year old grandaughter & I were out watching the Harry Flatters Rally on Epynt in the pouring rain yesterdy - Escorts, Minis, Avengers, Cortinas, TR7s, an M3, Delta Integrale & many others being thrown around teeming wet tarmac stages - wonderful !!
But, I'll say it again, each to his own....