How is "touring" prius different from regular prius?

The G2 Touring had 16 inch wheels with wider tires, a rear sway bar and different shocks.
There is no G3 Touring model in the USA. Canada has one but I don't think it has any suspension differences.

Toyota (TRD) does market an add-on rear bar for the G3 that does make a real change in performance (cost about $250).

 

Gen 1 had no touring package. It began w/07 model year. See 2G Prius (2004-2009) Standard and Optional Equipment (Some Countries) | PriusChat.

I'm pretty sure there was never a touring variant for Gen 3.

 

The larger spoiler may be more efficient than the small one. The spoiler is not about down force but to break the airflow over the roof from the rear of the car giving less drag.
The wider tyres having more air drag is true, but this is not the only factor.
In the UK and Europe all gen2 Prius come with 16 inch wheels and 195/55/16 tyres.
All car tyres now sold in the UK/EU market (even those on new cars) have to display the rolling resistance from a standard test. Going to the next size up 205/55/16 shows that for the same make and type of tyre in the great majority of cases the rolling resistance is lower, and in non does it go up.
I use 205/55/16 tyres and have shown an improvement of 3 mpg over the 195 section tyres.

John (Britprius)