sms777 - thanks for the english comprehension assessment.
You're correct, there is cause for concern that equipment like Garmin glass to have reliability issues in the conditions you list - likewise, analogue gauges using mechanicals are probably more susceptible to humidity,sea water, dust etc than solid state units.
With the Garmin (or avidyne) GA glass systems, key components like the Attitude Heading Reference System, Air Data Computers and PFD's are line replaceable, with the PFD's having reversionary modes (like neville mentioned) and redundancy in the electronic units (some setups use multiple GPS receivers).
Overall, for the kind of flying the Twotter does, having a good integrated dispay/nav system - in my opinion - outweighs the reliability issues.
I haven't heard or found any concrete evidence that states the glass systems are
less reliable than traditional AH's and RMI's - and I'd be glad to be pointed in the directions of such.
Insofar as my comment about this sort of equipment becoming standard - most new aircraft are being fitted with these systems, and the analog gauges used usually as standby instruments only.