Hey man, don't get frustrated. It's great thet you are out flying making observations and coming up with conclusions based on what you see. Then even better after you make your decision you come here and share your experience with your fellow modelrs. You wont always be right and others will chime in and let you know. Some of these guys have been flying longer than I have been breathing (36+ years) and the fact that they are willing to share with us commands our respect and attention.

Now for my OPINION on your situation. Yes it is posible the aluminium spinner saved your engine from damage. A aluminium spinner will be more likely to glance off of rocks and other more dense matter as your model attemts to bury it's self spinner first. However A plastic spinner will "soften" the blow by absorbing some the energy of the impact as aposed to transfering the energy directly to the crank, front bearing and engine housing. The best meathod for engine crash protection is don't crash nose first... Yes, I understand you had no control in this case; just being a S/A.