Question 1:
Be sure you did not set "Set 0 => no 8bit alpha (all stencil - yuck)" in Fgraphics.cfg file to 8. With some graphical card, it's the best way to have background objects in front of front objects.
Else, the solution lies in the texture format. Try to keep only one DXT5 texture and convert other textures to DXT1 (in your case, the tree texture should be DXT1).
Question2:
I have to admit I never saw this case where only parts of an object were missing in game. As visibility settings apply to a whole object, it's either the whole object is missing either it's there...Well, it might.
Concerning features:
1. Garages are along 33 sectors and thus without cmagic changes (that 3ded can't handle), and with first sector being sector 0 cars might be on top of the wireframe line of sector 1&2, 4&5, 7&8, 10&11, 13&14, 16&17, 19&20, 22&23, 25&26, 28&29, 31&32. Pitbuilding walls/pillars just lie in other sectors (0,3,6,9,12,15,18,21,24,27,30,33). I'm maybe wrong anyhow.
Anyway, as I can't handle cmagis values for now, I can't represent any correct car position for pit cables positions for example.
2. To detch multiple faces, you would need to click on every line (face) to highlight it in the 3d display, then note which faces you want to detach, then select only the faces you need and finally detach them. Not that quick nor useful.
So there won't be multiple detach in next 3ded version but the way you select face and the way you can detach them to new or existing part will be easier and faster.
3. Sorry, I don't get your idea here. Detaching faces at part level ?? I assume you think about a special case/object needing such feature...
4. I'm thinking about a form of change propagation but not exactly the way you describe it, else you will have "aliased" track elevation if you understand what I mean (ie, 20 sectors at height1, 20 to height2, and so on...). Anyway, for now, Track Profiler might not change in next version.
That's all. I know I promised to release next 3ded soon and from the 4 questions above, you may think very few changes will be in next version but that's not true, next 3ded version will be a major step above 17.6. I'm really working hard on it and I finaly added some features I dreamt to add since the very first version, without counting the numerous great new features, enhancements and fixes. Believe me, Track creation will become much much easier and faster and tracks created will be even better.