Mine varies quite a bit between ranges. If I zero it on the 1V range, I get a 400mV offset on the 2V range for example. My experience with analog electronics makes me think it is unlikely to drift much with temperature, particularly over the ‘operating range’ of a human being, who must be operating it! Although the TL082 doesn’t have the best characteristics… Drift with time may be experienced, but this is likely to be over a very long period (years).
I would personally be very happy to calibrate the necessary points - particularly if I only had to do it once. What may be worthwhile would be to use an average of calibrated ranges for the cal of any range the user neglects to do.
I personally think it IS worth the effort. I hope you will consider it further!