You have to consider what it takes to do a mod car compared to original car labor/cost wise.
Original car you just remove and replace back with its replacement part.. No creativity/innovation or enhancements. That’s where the expensive comes to play.
If we were talking about a DB5 Astons or 275 GTB 4, cars with production of less than a 1000, of coarse you would want to keep its originality. Or if you have an original Bugeye that say was the first car or the last car produced kept in the museum for sure it should be kept original.
Lets not forget that Sprites were made cheep for the starter sport car enthusiast..
Look in the original parts catalog. There is a whole chapter of performance parts provided by BMC. You had springs, camshafts, sway-bars, shocks, wheels, exhaust, carburetors, distributors, and may other performance components. Donald knew that racing and performance parts would enhance the Bugeye Sprite owners driving experience. He even showed the world how well the cars would perform when he showed up at Sebring in 59.
Much rather have a resto/mod than a car that will barely stop, has no power, body roll to the hilts. 43 hp with 52lbs of torque, 0-60 20.5 seconds, man that’s eating some asphalt for sure. Usain Bolt could beet it in 100 meters.. “NO” I’ll keep my resto/mod while keeping looks all British.