I'm a current Irish JET in Gunma! The stats for last year were a total 206 applicants in the first stage, 70-80 to interview (this was due to cutbacks), then 42 were selected but only 39-40 went in the end due to a number of things.
I don't know the figures on the numbers of Alternates that were upgraded, but the impression that i got was that about 5 people including myself were upgrades.
Keep the faith man! I applied first the year before last all at the last minute and didn't get the interview: but the following year i set myself a goal and here i am!
(with a bit of luck too)
Remember what they're looking for undying love of Japan that will make you stay there at least the length of a year contract and what YOU can give to Japan. Then again they don't want people are want to spend the rest of their lives out there. Its all about GOALS, what you want to go and do, how you want to do that.
If your thinking of applying again, its possible you might get it, its also possible you might not. ALWAYS give yourself a backup plan and seriously life as a private ALT isn't that different from JET ALT, there are racks of jobs out here especially after the earthquake that can be yours for the taking if you keep a good head on your shoulders.
Above all else believe in yourself, trust me its not easy but with your feet on the ground before something big as moving to Japan, believe in yourself
Hope that helps man!