Having a precision reference means your ADC will give a more accurate result, but what happens when the battery for the sensors drifts? The output of the sensors will drift by the same ratio and thus you will have an imperfect measurement. Thus the beauty of ratiometric measurement.


As for amplifying your sensor signals - you will also amplify the sensor noise - if the signal resolution you want is buried in the sensor noise then you'll be unhappy with the result. As Kai mentions, you've also got temperature drift issues etc, the higher your amplification, then greater your temp and drift issues will be. You'll have to read the sensor specs carefully to understand what they're capable of rather than what you're hoping for.

If you want to create an offset in an op-amp circuit - just have the virtual earth adjustable with a trimpot - no magic required.

Input bias (or offset) is the current the op-amp imparts on the input signal - this differs depending on the op-amp. This is why you have the same resistor values on both inputs to counter this effect. This differs from the offset you want to create.