Powering 3.3V I2C from Arduino 5V?
Using a voltage divider to generate a power rail is most often a bad idea, as you don't know what your current draw is, and you don't know if it will be a constant current draw.  Think about how inaccurate your divider will be with a circuit sucking 20 milliamps from it.  It's a calculation worth doing.

This is what voltage regulators are for.  Try http://www.mouser.com/ProductDetail/Microchip/MCP1702-3302E-TO/?qs=jZi1jxfVU95RAHKJCz8stQ%3D%3D&amp;gclid=CMyooOLjss4CFdcZgQodzxQCBw  for a 50 cent part  -  but you need to verify that it can deal with enough current for your purposes.

As to whether it's worth your time to dork around with your board/shield, thats up to you.