About the undo issue, when it doesn't work... please try clicking the button instead Ctrl-Z, and tell me if there is some difference. I want to check if it's a problem with the hotkeys.
there is also one more problem with spinners - when click it and drag up or down - its value updated in weird way, with some gaps or only when finish drag
Probably is caused by the lag between the editor and Max. We'll try to improve it.
1. disable, but not delete node. will be useful for Reverse and Mirror nodes
Ok. Currently this feature is implemented only for Generators.
2. select in scene Segment or Spline object from node context menu
Already done. Right clicking on the RailClone object, you will get a "Select RC Base Object" menu with three elements. Unfortunately it's not possible to change this menu dinamically, so we fixed it to the first three Base Objects.
About the segments, it may be more problematic, because RailClone can use embedded segments (without nodes in the scene).
3. create Generator node with empty Spline and Segment nodes attached
Ok. Each generator can use multiple Splines and Segments, but we would add a "Basic Template" option to add automatically the most commonly used elements (i.e. one spline + one segment).
4. name Spline node according spline object name (same as done for Segment nodes)
Splines are not renamed automatically, because usually they have a fixed name assigned (as "X Spline", "Clipping Area" or whatever else). It's not a good idea to overwrite it when picking.
5. Surface node either as Generator or as Spline input. in order to project Spline node on it.
Yes, we have some ideas about this in our wishlist.