rear suspension with it's rigid tension bar.

If you go into the Mods forum and search on "rear anti-sway bar", you should find at least one long thread about putting them on 2010's. I bought a Toyota one intended for a 2008 Scion xB which is apparently identical to the one in the Prius Plus package. There was discussion about just how much an additional sway bar in the rear would help, and it does seem to help though a double-blind test with two vehicles, one with and one without, might be interesting.

 

A lighter wallet can lower the total load on the vehicle and improve handling.

 

On the rare occassion when I take my wifes Gen 3 for work and she has to drive my Gen 2, which used to be hers 3 years ago, she always complains about "how hard I am on cars" and "The ride is a lot stiffer and the steering is too tight". Maybe she suffers from pre-placebo effect since I've never told her I added a stiffening plate and rear TRD sway bar. I'll tell her what I've done one of these days so she can be downgraded to just placebo effect.

 

Well, yes, I'm talking about my Gen 2, not my wife's Gen 3, but you can understand my confusion since you said in your post "This reminds me this old story on placebo effect in 2nd gen Prius (scroll to the bottom 3 paragraphs):"

 

In that case, my prius should be floating in the air like a hovercraft. :0 lol