My mileage with 75% city 25% highway was always 18-19 mpg. Now that my commute is really short all city, I am seeing 16-17 mpg. I was thinking something might be wrong, but I think its just my heavy right foot. Since I did the PNP headers and X-pipe the car pulls nicely and I am in boost all the time with my Stage 2 E-tune.
I say a tune is always worth it if you are keeping the car for a long time. Think about it $500 bucks over 5 years is nothing for the improvement. At least an e-tune, never OTS.