Crazy boost they may leak. Not a big fan of blow off valves personally. Especially when the relieve to the atmosphere. And double especially on a MAF car like the GT-R.
That air has already been metered and when you release it - what does the computer do ? Well its supplying you this much fuel for that much air. So it goes rich. When it goes rich the 02 sensor says its rich - I need to be lean... leans the mixture... then some detonation - then you are rebuilding your motor. Well a possibility anyway.
I would say though--- above 500hp levels you want to have a hard look at the blow off valves... You probably want to pressure test them at the least.