The sensor has incredible resolution and is only limited by the noise level in the complete system, probably the AD converter of the microcontroller, band width at the sensor is theoretically infinite using DC excited bridge, the limit will be the microcontroller sampling rate, it will be well beyond the response of the servo system anyway as this will be the response time limit due to the motor inertia.
Using shielded cables and shielding the sensor grids the noise level can probably be ignored for this application, the trick is to raise the torque locally by reducing the shaft cross section where the sensor is mounted and use a reasonable exciting voltage say 10 or 12 volts, the voltage is limited by the gauges ability to sink the heat into the substrate, using an aluminum tube and a gauge with a decent grid area lets you sink quite a bit of power without the gauge heating and possibly drifting - we are in the world of instrumentation quality measurements at this point

and probably far more accurate than we require for a controller.
As an aside, side sticks for combat aircraft use strain gauge technology as a more reliable method of measuring input forces rather than just displacements.
Last time i looked you could get foil type gauges from RS, low noise, low offset, high input impedance op-amps are cheap and easily available these days, so its doable for home engineering.
The sensor could be used to generate the servo demand vs torque base calibration as well to give you your base values to offset rider input.
Google 'strain gauge shaft torque measurement' to get an idea of the arrangement, its not as complex as it sounds

and has been used for years.
The big advantage of this approach is you get a true torque measurement, trying to use load cells you will have to resolve the turning moments and you get errors from bending forces etc.
edit:You can get strain gauge bits on the but, but noticed these..
http://www.hella.com/microsite-electronics/512.htmlThey use the 'skin effect' to sense the stresses in the steering tube and output angle and torque for electric steering systems, looks like you could pull one from a scrasp car to try, seems vauxhalls and fiats use them in the power steering system so i guess many others as well, some on the bay for merivas have the complete mini colum so would probably be a good starting point.