Went this time last year, spent a week driving Ebisu, 2ish days in Tokyo, 2ish days in Osaka and a few days in amongst that touring the countryside.
You need to go for a few weeks to make the most of it. Will be going for three weeks in November next year - not doing any drifting - to make sure I see everything.
Make sure you take a mobile/tablet with Google maps. Forget that Apple junk, you NEED google. Speaking from experience there, as my friends couldn't find anything on apples latest and greatest. Just type what you are looking for into gmaps in English, and it will take you there. Just don't go looking for ARC as you will end up in a rice paddy.
You wont get a mobile or similar while you're there, so work out a WiFi dongle before you arrive (I used e-connect Japan).
Proof of awesome J-land trip, Daikoku in dori cars
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And Shibuya Square (terrible pic is terrible)
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