I've seen these Helix throttle body spacers for around $95. Are they worth it?
I have a CAI, if I add this will I get even better MPG?

If I add steel headers and 2 1/2 inch pipe to a 4 inch out performance muffler and a CAI and throttle body spacer, will it be too much for the 5SFE to handle?

 

Your stock setup was a CAI. You gained nothing by adding an aftermarket. Headers should improve flow but without engineering data you'd be guessing on size of pipe and muffler and if aftermarket CAI was necessary. Not sure what you want to gain with throttle body spacer since engine is fuel injected. Trying to do what you are doing will not increase gas mileage as you're trying to add power and power equals more air, more gas, less mileage. I'd go to Toyota Nation where some members have actually done what you are wanting to do and may be able to give you the actual results.