Thinking about seeing EXO in Japan but want to know if the GP has any significant benefits
The biggest benefit that you'll already have is being able to get tickets to see them! It's almost impossible to get tickets to a concert in Korea or Japan unless you're either in the fanclub, buy tickets off of a reseller website (and risk them being fake and getting turned away at the door. Or even being turned away because some tickets will have the original buyer's name on it) or by purchasing the global package that SM offers for their artists.
As
@RandAlThor has already mentioned. I've previously purchased the GP myself for Taeyeon's concert in Seoul and also for Red Velvet in Japan and I would say that it is worth it!
You will get great seats (I've always been close to the stage), you'll be put up in a decent hotel and you also get other benefits such as some food, merchandise that's exclusive to the package and also another great benefit of being able to preorder the tour merchandise. Which is great, because you don't have to worry about the merchandise that you want being sold out.
The tour guide that SM assigns to you will also be with you as transportation that's been put on for you will take you from the hotel to the concert venue and back to your hotel again once the concert is over.
And depending on which package you purchase there's sometimes other benefits as well such as a tour of the SM COEX (if you're in Seoul), tour of the stage that the group will be performing on and sometimes a day tour of the city that you're staying in.
(And if you're still unsure. You can risk spending upwards of $300 for a ticket on reseller site and risk it being fake. But with the GP you be at ease knowing you can get in)