Personally, I think it would be extremely beneficial for them to promote globally. I doubt that there won't be any extreme increases in sales and whatnot, but it's definitely not going to hurt them.
However, in order to do so, I feel like their events need to be better. These worldwide handshake events don't seem very fun at all and they're poorly timed. It's mainly the management that's been ruining the events. I haven't actually attended any of the events, but out of all the worldwide events that they've had, it seems like the trip to Anime Expo in 2009 was probably the most successful. Having a live concert definitely boosts interest. Of all the H!P events out of Japan, I'd say that one and the Buono in Paris event succeed the most. I guess the Kikka in Atlanta event was pretty successful too, but sadly, there's not too much hype out her.
Then again, I've only read fan accounts, so I can't be too sure. They just need to get better management if they do decide to branch out (such as not screaming at the fans @ Berryz in NJ or unclear amounts of handshakes)
BUT, if we do want to see more of Morning Musume (other other groups) out of Japan, the fans have to contribute too but actually going and making the event as successful as possible.