If we use the AFNFL calculator, kicking off gives us a WP of 0.02 (assuming a touchback, which it usually is with the hands team). If we onside kick and get it, which is ~20% of the time (albeit under the old rules), our win probability is .13. If they recover it, our win probability is 0.01. Therefore, the EV of onsiding is 0.2 * 0.13 + 0.8 + 0.01, or 0.034. That's an almost 70% improved chance of winning, although I'd imagine there's a fairly substantial margin of error with those calculations. Still though, it just doesn't make much intuitive sense to trade ~30 yards of field position for an almost 20% chance of getting the ball.
Edit: As I see there's some discrepancies between onsides data, ANFLS has it at 20% for non surprise onsides.
http://www.advancednflstats.com/2009...ide-kicks.html