I also have a RS4 RTR 3. It is a very durable car and makes a great parking lot basher. However there are a few things that need to be addressed before this car really performs well.
The stock header is crap, you will need to replace this. I went with the THS racing one piece header and pipe.
The single needle carb, also crap. I put an OS 10e carb on the stock hpi engine and it has been running great ever since.
On the plus side it is a shaft drive car, much better for parking lot bashing and racing imo as opposed to belts.
The stock engine, although not a rocket by any means has performed exceptionally well, I have lost count of how much fuel I have run through it and it is still going strong, fires on two or three pulls every time.
As far as durability, I have had a few pretty bad crashes, and had very minor damage.
I would recommend the RS4 3 SS over the rtr, but you will then need to add a radio and servos.