So maybe the waitress was right?
Everybody else went faster than the week before. You did not - that makes me think the slicks are dead......and of course you're pax number is terrible with them.
For Kelowna a shorter tire is better on almost all cars.....actually every car I can think of except maybe a Mazdaspeed Miata. Tires are really just another gear - shorter is better acceleration with the added benefits of lower unsprung weight and lowering the center of gravity. The MR2 should be on 205/50/15 - that's my guess anyway.
Good luck with the volley ball girls