I am currently looking at an ebay listing for a Japanese sealed ex series box on ebay. I never really deal with sealed products or Japanese cards, so this is really out of my wheelhouse. Do sealed English products generally appreciate faster than Japanese? Is it the other way around? Does one generally have a much lower supply/market? Any info would be appreciated.
English has much higher supply (as far as I know) and much higher demand. The Japanese items are quite niche as well.
Like with some of the Japanese Gold stars, I believe the EX series product for Japan hit a high point (at least relatively) like 5 years ago, and now English product appreciates quicker.
Certain Japanese packs are still worth more than the English for EX series. And some particular Japanese products are almost impossible to find, such as World Champions Pack (their Power Keepers). As well as the Rocket Gang Special pack with the deck and booster packs.
Stick with your English until all your goals are met. Then you can always jump on the Jpn train;)