You probably won't need the 2 up rear springs, and with the adjustability of the Fox 3 up front I don't rember hearing anybody saying they were going heavier springs.
Only mechanical issue has been reverse but that was corrected with an update that keeps it from popping out of gear.
The 2014's have had a few electronics issues, not significant that would strand you, but hard starting warm and a couple others, the 2015's will have updated ECUs. We're hoping the 2014's get the same software updates.
Many site members have turbo charged their Vipers and a large number of those owners are riding big miles with little or no issues on the engine, drivetrain, or chassis. Spend a morning or afternoon on the site and check out some of the comments other users have made would be time well spent.
We have his and hers Viper LTX models and love them.