My understanding is that in Europe (where sedan racing has always been more popular, compared to here) the NSU 1000 TT is apparently a fast little car for it's size and ideal for racing.
Not sure why they never used the Sport Prinz for racing??
I did spot this Sport Prinz here in Calgary a couple of years ago, it's gone somewhere else now but I don't where... And note how small the car is
Also regarding the wankel-engined NSU's... I thought I read somewhere that the Wankel Spider was essentially a test bed for the rotary engine (even though it was sold as a production car) before they came out with the Ro80... And that (much like with some other classic cars) enthusiasts have ironed out the issues with the NSU rotary engine and made them more reliable these days.