I have seen q few Rallyes now going for around £1500 but the reason for it is cause the shell is in a bad state, sills etc. rust so when they do get that bad they are really only worth what the engine and 4wd is worth.
The reason behind the Rallyes and rust is if they haven't been looked after well, the arches sill etc... came from motor sport factory and there they don't do as good a job as the main vw production line thus teh rust setting in earlyer.