As if the performance and handling of the (car) isn’t exciting enough,
or
As if the performance and handling of the (car) aren't exciting enough,
Which is correct, isn't or aren't?
aren't
As if the performance and handling of the (car) aren't exciting enough,
"performance and handling" are two items. replace with "paint and stereo" and aren't sounds just fine. Mentally we group performance and handling into one idea.