For individual spacing adjustments the blue handles have their fixed position above the staves. When there are notes in that region they partly get covered by the handles and it’s hard to see what the adjustments will look like. In order to have a clear view on the distances between the notes I’m forced to quit the note spacing mode. This on and off switching of the blue handles is okay for a few times, but rather time consuming for adjustments of a whole score. I guess there’s no workaround for this at the moment, but may be for a future update it would be great to have the handles act intelligently, so they avoid collisions with notes.
This doesn’t really help the problem but zooming in considerably should make it easier to see the results of your adjustments. On the other hand, if you’re making large numbers of these adjustments, it might be better to try to find settings which would prevent your having to make [most of] them.
Thanks, Vaughan. Zooming in helps. As for your second suggestion: I love fine tuning, even with good settings. Once I get a job to set the Urtext score for the Goetterdaemmerung or something alike, I will refrain from fine adjustments 
Note that you can set keyboard shortcuts for Graphical Editing mode and Note Spacing mode. If you’re frequently flicking in and out, it might be worth setting these up.
Oh, come on, why not just set the whole Ring while you’re at it?
The whole Ring? Now that you suggest it… 
Yeah! I will defenitely do that.