Generally Sportivo is geared to the casual driver looking to upgrade a touch above OEM (aka OEM+) also available for Toyota non-sports cars. Think I've seen a marketing video demonstrating a tighter line through a corner with reduced body roll and, hence, improved safety (for a Prius, I believe). I had the Sportivo kit (springs/struts/sway bars) on my MR-S/MR2 Spyder. Felt great on street and didn't scrape on driveways.
Not sure on why the increased rear stiffness. Making the rear easier to unsettle is kind of uncharacteristic. Maybe it's supposed to work in conjunction with the sway bars (if they do offer sway bars for the 86).
