People seem to be touching on it but here's my $.02...
The track is where you can learn how your bike acts at speed. You become AWARE of what it feels like at more extreme lean angles. You grow MORE accustomed to approaching corners at higher speeds. You BEGIN to learn how to navigate these new situations and instead of panicking, you learn to ride through it and do so enough times so that you gain some familiarity.
Does this teach how to deal with sand in a corner? No, not explicitly. However, it gives you the tools to do so. Instead of being afraid because you're approaching a corner quicker than expected, you say "I'm going too fast for the street, but I've seen this before." You turn in, see the sand, and again instead of freaking out you say "I'll just change my line mid-corner."
No the track is not a substitute for street miles, but it WILL go a LONG way in giving you the tools needed to ride safely. Probably faster than you used to, but more importantly, safer, because you know what to do and have proven to yourself that you're capable of the maneuvers necessary to come through tight situations in one piece.
Troll.