I have owned a JDM for over a year now and am very happy with the car.
There isn't too much in Japanese and all of the major buttons are in English. It is mostly Sat Nav buttons in Japanese (that doesn't work here anyway).
I think the decision depends a lot on your personality. I like being able to service my car where I want, put an exhaust on the car, use a different transmission oil etc. without the fear of losing the warranty. I don't have a warranty, but I didn't pay for it!
If you are going to track an ADM car often, you will need to take the car in for pre track and post track inspections and change the fluids with Nissan (expensive) items to maintain your warranty with respect to those parts.
Bear in mind that if something does break on a JDM, it may be expensive and time consuming to repair. However, there is some excellent after market support for the R35 in Australia now.
I would recommend that you talk to some of the workshops who look after R35s to see if you are comfortable owning a car tha Nissan may refuse to support or service.