Our cars are 2nd generation G's (MY 2007 - 2010).

 

I ran same springs on my G35 with stock shocks and the ride wasn't that great at all. Wasn't valved to compensate for the springs. Ended up putting in Koni's and all was fine after that.

 

+1. The Eibachs arent much siffer than the stock setup, so there will be a lower life expectancy, but it will be minimal.

The comparison to the Civic and its life decrease in shocks is the extreme case. If you go from a shock valved for comfort and put springs on which lower the car and change the springrate significantly, you are going to see a huge decrease in the life of your shocks.

The S springs are already pretty firm, so going from them to Eibach's only lowers the car a little and increases the springrate a little, so the decrease in life expectancy will be much less than the scenario involving the Civic.