Hi 
I've not yet done Ben Nevis via the Carn Mor Dearg, but understand it to be fairly straightforward with the added bonus of impressive views of the Ben's North face which are not seen on an ascent of the main tourist path.
Re Crib Goch - particularly for those who haven't yet done it - although the 'fear factor' can be very subjective, I consider that aspect to have been somewhat exagerrated by walkers/scramblers in general. After my first go, having sat astride the main part of the ridge and nervously shuffled along, I concluded that it wasn't quite as terrifying as many had made out. If anything, the ascent of the East ridge was more challenging.
On my second time, I was far more confident, even walking 'no-hands' along the top of the arete at certain points. I imagine that you might be somewhat bolder on another attempt.
But like I said, these things can be subjective. Nevertheless, Crib Goch should never be underestimated. It IS dangerous.
Best wishes