How do I scale a 0.5-4.5v signal to a 0-3.3v signal?
A simple potential divider rescaler would only be "throwing away" (0.5 / 4.5) = 11% of the resolution.  To me it seems likely that the simplicity of the potential divider (vs the minimum of one op-amp + passives that would be needed for an active analog subtractor) is worth it, especially when you consider that the additional circuitry would introduce some amount of noise and scale/offset error.

As a bonus if you preserve the ability to read below the sensor's minimum specified output value, then you may be able to detect a failed or unconnected sensor.