The full plus kit has the following:
-Bodykit (sideskirts, front lips and rear bumper underskirt in colour)
-Recaro seats with red stitching (also on steering wheel, gearstick and door panels)
-Red strut brace
-6 speed gearbox
-Starter button
-Brembo brakes in red (normal is silver)
-Red engine cover (Testa rossa in italian, sounds much better
)
-Silver dials
-Luggage net in boot
A lot of these things were put on the normal late 20vt's as well, so not always exclusive to the plus. The late models (including plus) also have a interior light in the left c pillar, a FIAT logo stamped in the kick plates and there are panels behind the centre console (on the sides) that make it look a bit neater.