Well Alan I am only 24 and this is my second season of riding...so take all I have to say with a grain of salt
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As I continue my research and talk to the guys I ride with, the consensus is to go for fit and comfort above all else. You'll be looking at helmets made with different shell materials; polycarbonate, carbon fiber, organic fibers, injected Lexan, etc. etc. This plays a big role in weight reduction, but if it passes DOT, Snell, or even ECE (Euro standards) you'll be doing just fine. In addition, it is the EPS liner that does the bulk of the work if you're in an accident, as this is the energy dispersing foam that helps cushion the blow. I believe all helmets are using EPS (extruded polystyrene) but I'm not certain.
Beyond this it becomes the land of options; noise reduction, ventilation, comfort liners, washability, adjustability, style. I'd argue the optimum range for quality and features is between $350-$400 (street prices, not MSRP). Shoei, among a few others, is going to be your top-of-the-line stuff and many members here can argue on behalf of their reputation. I'm currently in the phase of finding numerous brands and testing out the various models and styles; being my first helmet purchase and all.
Dukie, the RF1100 was a sweet full-facer. If I decide to drop my modular thoughts, I am aiming straight for that.