Depends where you buy it from.. There's a 15$ price difference at newegg (i7 930 at 284$ and i7 950 at 299$) and a 30$ price difference at microcenter (i7 930 at 200$ and i7 950 at 230$)..
You are getting a 13% increase in power (Clock) for a 5% price increase. Yes, its worth it.
It is actually a 7% rise in clock speed for a 15% rise in price (considering microcenter prices) and approx. 8% rise in price (considering newegg prices)..
^I was considering newegg and assuming the prices for the 930 is 284 and the 950 is 299. Check your math skills buddy And I did approximate but your numbers are still way off if you saw the same prices I did.