No tuning it out won't affect it at all. Maybe a few mpg but if you get the tune you'll gain a few mpgs so it'll even out. If you get the emulator then it might affect the mpg a little. Since you don't have emissions you'll be fine.

What years is your car? And what engine?

its a 98 with the 3800.

does the 3.8 have two cats? basic tune with solomon is 85 bucks. give him a call or email him. great guy to work with.
http://www.lt1pcmtuning.com/service/#Basic

No the 3.8 only has one cat. Wow that's pretty cheap for a tune.

I'm thinking if the basic is $80 but the power tune is $110 that I should spend the extra $30 for more hp, torque and mpg.

and you can update it once for free if i remember right. i still have a update coming just havent had things right to do a data log.

Do the power tune since you are getting headers and have a cai on your car. It'll unleash more power.