I had the same idea, but it is indeed really much work to do that correct. It may sound simple to some to create dents as it doesn't need to fit any form or patern, however exactly that makes it difficult.
For example if a car crashed into a tree the dent is not an exact match to the form of the tree. Also making the materials nicely random is time costly.
However a few (in my case T3's) without bumpers/doors/tires etc. are an option I may go for.