I agree with you Richard, she looks very cool. However, the white circle on the door is a very clever touch. Maybe find a roadster on the net that looks exactly with black alloys like this one in black colour but without the white circle. Then you can see if it still looks as cool or if it might be a bit drab.
In no case would I take smaller tire sizes and if at all then only bigger and not smaller ones because of the low ground clearance of the Roadster at the oil pan. MMC changed from 205/60/15 to 205/65/15 with the introduction of the Roadster Sport in 2010.