The front flanges where the retainer spring clips go on will sometimes deform in a crash with the alloy, but does not in steel. In the rear because you don't have steering this does not happen. Some people have problems with wear in the cross pin holes in the alloy ones but this is normally after quite a few packs 200+. On my original T1 the rear axles did not show any real signs of wear even after 300+ packs!
With the C-clips- they are designed so that you have to file the 4mm down to fit. I real pain I know but if done right you can get free moving A arms with 0 play!
The conversion to C hubs in alloy is lighter than the original PB suspension...I blame those heavy PBs!
Do you have the graphite upper bumper piece, or the newer plastic ones? For the grpahite one can break in a crash. Different people have different solutions for this. I double up the graphite piece and have had no problems.
Also the weakest spot on the car is the rear edge of the bottom chassis! Xray now have a new plastic rear bumper piece to protect this....if you do not have...buy it!