Ask any lorry driver, a small amount of run out can cause enough steering movement to create fatigue over time. 1mm is not too much, however I would do something about it, even though it's not as bad as an unbalanced wheel.
Whire wheels are difficult to "true" but not impossible by a skilled person. You could try out a decent motorcycle wheel specialist. For adventure touring on motorcycles, a favourite has long been "
Woodys Wheel Works"
They do car wheels as well, but shipping can be costly.
