Regarding damage carry-over, the reason they can't carry over damage to another race is because its procedural and real-time - your car's shape and specs at the end of a certain race would have to be carried over, and since it's not pre-canned, for each car you would require more memory to do so, which is not possible because:
1. Hardware limitations (PS3 may be a killer machine but it still has limits, especially in RAM)
2. The models are very highly detailed and therefore are obviously very large files.