It's hard to have any objective discussion on the topic, because just about everyone has a bias that they want to justify. Someone who doesn't feel like they date enough will find comfort in blaming the culture or other people for not finding them attractive. Someone who does feel like they get enough attention doesn't want to diminish themselves by letting something like ethnicity take the credit.
Still, it's easy to see that anywhere in the world, exoticism always makes someone stand out. Being the only non-Asian in a room full of Asian people will stand out just much as being the only Asian in a room full of non-Asians. Eye color, hair color, height, or anything unlike the people around you will make you easier to notice. The very word attractive means "to get noticed and desired by others," so standing out gets half the job done.
Also, it's easy to see that being noticed and being wanted are different. If you had a horn on your head like a unicorn, you'd stand out a lot, but a lot of people might just think that's a bit too weird for them when it comes to who they think of as date-worthy. Being noticed is only half the battle of attractiveness, you have to also be desirable—and that's where things get a lot more complicated very quickly.
If you liked tall people, you might go up and talk to a tall person. If they were verbally abusive, that would eradicate any appeal of their height. Any positive trait can be wiped out by negative ones, and so it goes with foreignness. Just as some Japanese people might find stereotypical images of foreigners attractive, others may find language and cultural differences to be mendoukusai (too much trouble to be worth it).
All told, foreignness, simply as a form of exoticism, might be one extra card to play depending on who you want to appeal to. Dating and finding someone to be with is a challenging game, so any advantage—no matter how slight—will come into play. But, it's not a trump card by any means, so don't get the impression that anyone can win the game based on that one card alone.