Poor man's voltage reference
You can calculate the worst-case output error by adding up all the sources of error and assuming their direction adds. 

Initial resistor error, temperature, time drift of resistors (also moisture load life), offset voltage of op-amps, temperature drift of op-amp Vos, op-amp gain vs. loading. Reference error and temperature coefficient. Noise of op-amps, resistors, power supply and reference may also be considered. Voltage coefficient of op-amps and change of reference voltage with supply change. You can buy matched resistor networks so the temperature coefficients and values are matched to each other but they're a bit expensive. 

Downside? Power consumption, possibly more noise. Hand picking 1% resistors is not a very good solution compared to buying precision resistors in the first place. If you absolutely must, use matched resistors from the same lot. The calculation won't show the improvement however.