JRA does not mean you can't do some intensity stuff. You can do tons of SST type riding within the unstructured riding world. It's really how I've come to spend my base periods as a whole. 2 days per week I do a 45 min - 1 hr hammer session. As the off season rolls on, I may lengthen it to 90 min or even 120 min, but pull back on the intensity a tad (ie 85-90% vice 90-100%). Longer sessions aren't as penalized by brief stop lights, turns, traffic, etc... These fit much better in the JRA concept, and don't nearly wear me down mentally as much.

Once you drop to the 2x20 or 3x20 world, mental fatigue will begin to set in - if you're weak minded like me.

I'm in a similar boat. I unplugged my season in the beginning of July, and now my next "A" event isn't until May 3, 2011. I'll get a little bit of racing in before that, but a lot more sparse in Japan than it is in the states (ie 3-4 races total between March and May, vice the 2 races/day on both Sat and Sun for 6 weeks straight) I'm riding as much as I can. If I get tired, I take time off. Then I get back on and ride as much as possible again. It nets me 19+ hr weeks right now with 2 days per week of SST. That's commuting to work every morning (true JRA) and a good training ride on the way home. Doing good max hours also ramps the metabolism up like mad and I can quickly outride my appetite, facilitating good weight loss where that fatigue doesn't interrupt my intervals.

I would definitely stick to the unstructured, ride as much as possible and don't worry about fatigue.