Nonsense question. Why should a car be considered "feminine"? A car is an object designed for mobility or, in the specific case of the Mazda Roadster, for driving at a sustained pace over public roads and racing venues.
Is the Roadster a car designed to appeal to women, and therefore feminine? I don't think so. The Dodge LaFemme was a feminine car. The Honda She's is a feminine car. The Roadster was designed for enjoyment by people who intend to a)drive fast, b)drive with the top down, c)not spend a lot to do so. The gender of the driver wasn't taken into account, I presume.
Is the Roadster a car driven by women? Are cars driven by women feminine? Then this...
...and this...
...and this...
...are all "girly" cars, because they've been driven by women (respectively, Lella Lombardi, Michèle Mouton and Sarah Fisher).
Is the Roadster for some reason (perhaps its lack of SHARP EDGES and ANGRY HEADLIGHTS and BRO INTAKES, or its relatively small engine) considered a "girly" car? Sure! Likewise, the BMW M3 is considered a douchemobile, the Subaru WRX STi a car for junkhead street racers who like to keep the neighoborhood awake with the obnoxiously loud sound of their exhaust, and 70s/80s muscle cars should be the preferred mean of transportation for the wife-beating, possibly meth-smoking white trash crowd (in the US) or for simpletons who are too much into everything that is 'MURICAN (everywhere else). Who cares? You know what you're driving, and why you're driving it. And all cars go to heaven, y'know.