Nothing to report, have past the 43.000 Km mark with the 500 Sport, and stil going strong.
Sold the original 16 inch wheels, and run summer and winter tires on the 17 inch wheels.
Circumference can be the same with lower profile tires. There are tools available on the worldwide interweb to help decide which size will be (almost) the same.
A week a go, the 500S got serviced at 45000 Km, incl: new front discs and blocks, and a rear hatch wiper.
Further nothing to report, still going strong without any issues, this is the best FIAT I ever owned.