I could understand importing D/P two years ago, sure, when it was brand new and we knew we'd have to wait so long to get it in English and EVERYTHING was so ZOMG NEW.
Now, with Platinum, we're getting a lot of neat-o improvements and a revamped story, along with some alternate forms and some new movesets.
Basically, every "3d game" ever.
I just can't see paying top dollar for a Japanese copy of a game that features 90% of the content you already own in English. There is no rush, to me, to own this. It will come, it will be good, and you'll get to understand everything. This, coming from a guy who imported Pearl the first week it came out.
Plus, unless you have a lot of connections, you might miss out on some rare stuff. All the official promotions won't be compatible with a Japanese copy! That means you might possibly miss out on the free Regis, Shaymin or "Rotom."