Hello!
Yes but where do you stop ?
This would be exactly my point. By far the most likely cause of death in any accident with aircraft (and road vehicles) are traumata, especially head injuries. So wearing a helmet would be the best measure to increase the odds of survival. But honestly, who does wear a helmet in a C172 or Pa28? And what about the passengers? Do they not have equal rights to survive a crash? (The same applies to the Nomex suit in my opinion: Either everybody on board wears one or nobody.)
In accidents involving fire, the most frequent cause of death is lung damage from inhaling flames, smoke and fumes. To protect oneself against that risk either breathing oxygen under pressure - military style - or PBEs (portable breating equipment) are the only feasible measures. Both are not suitable for single engine aircraft. It is _almost_ impossible to don a PBE inside the cabin of our light bizjets (I know because we have to train once per year) and absolutely impossible in the confined space of a Pa28. In my personal opinion, protecting your body against flames but not the much more vulnerable lungs does not make too much sense.
That said, I must confess that I too own a Nomex suit. I bought it on eBay (a grey ex german naval aviation suit for 20 Euros...) when I was involved in aerial work some years ago. We sprayed silver-iodide into CB clouds to prevent the formation of large hailstones. That chemical is only soluble in acetone (extremely inflammable) and leaves very nasty and almost unremoveable stains on every material that it comes in contact with (including skin and clothes and aeroplanes...). A Nomex suit seemed to be the right way to dress when handling that stuff. But I never flew in it, preferred to take it off before boarding the aircraft. Wouldn't have had any chance to survive a combined acetone and avgas fire in case of a crash anyway...
Happy landings,
max