Gah, don't make me paranoid again!!!
Like you say, a least it's an easy job... [bigwhistle]
The only issue with doing the sensor only would be 'foreign contaminants'.
That is, the loss of material off the sensor has to go somewhere. The only area that these micro shavings would go is in the hub .. most likely mix in with the bearing grease.
If you don't do the hubs at some point soon, I'd expect that it will start making noises sooner rather than later.
High speed bearings under huge loads and contaminants don't work together well.