I definitely think it's worth petitioning, if only for your sanity and peace of mind :)
My understanding is that JPN sales of Wipeout Pure were really, really low, I am not surprised that SCEJ is apathetic.
This happens all the time in reverse-- Nintendo and Sony keep many RPG and platformer franchises in JPN that I and other people would love to play-- but the companies think that localization and publishing isn't worth the effort. Look at Earthbound (Mother)-- that is a game with INCREDIBLY loyal fans, they actually created a book of original drawings that were inspired by the game, petitioned heavily, met with Nintendo Power people-- just to get Mother 3 (GBA) localized to North America. And nothing has happened, as far as I am aware.
Sorry, Hisho-- I really do hope the game is released in JPN, or at least, that the DLC will work with it...