I think it depends on how you come across. They certainly aren’t going to like an American accent when it’s being spoken by someone who’s smarmy. Most foreigners are grateful if you can speak their language, and as wildflower has already stated, the French aren’t always very appreciative of other languages.
But if you’re a decent guy, aren’t obnoxious or flouting about your Americanism, you’ll probably be fine. There’s no doubt that there are people who are decent enough to find it cute, although I’m not sure that’s what you’re aiming for.
I know France has a negative image with regard to anyone not speaking French, but I’ve been there three times vacationing, four weeks each time, and found that every single person with whom I attempted to speak tried their absolute best to speak English with me. My husband hated to admit it, and he told me not to bother speaking to them, because they wouldn’t even try, I never had a single person refuse. That’s not to say that it always went smoothly, at times I had to resort to using my hands, but they were all decent about it.
In the end, finding someone sexy has a lot less to do with accent than it has to do with personal charm.