IF you want a rear-drive two-seater convertible sports car under $80,000, only Mazda obliges, with the iconic MX-5. Now in its 20th year, the loveable roadster receives a facelift of debatable merit. But there is no denying that a more flexible engine, combined with slightly higher dynamics and improved refinement levels, is welcome, proving that the recently independent Japanese carmaker is not resting too much on its laurels.