Happen to still have your model? I know my way 'round blender, and can help fix it up for you. Because to me, it appears the problem is not in unity, it’s the way you have set up your models normals.
Reason why I say this is:
What you told us above is that you put in a couple of vertex splits to “put in hard edges.” I would recommend against this, simply because there’s a better way of doing this, and doing such a split would be bad for mobiles if you used several doors. Instead, I would have it so that faces that are flat on the door (i.e. not the grooves! ;)) have flat shading, while other surfaces (the previously mentioned grooves…
) are somewhat curved, so those can be made smooth shaded.
To do the above… (Assuming you are using blender 2.6 and up)
First go and make your mesh all-smooth again, then go into edit mode (the tab key’s your best shortcut! ;)) and select all the “flat” faces on your mesh. (i.e. the sides of the door, and anything on the front that isn’t a groove) Then press the space bar to bring up blender’s search box. In the text field, type “shade flat” and hit enter. all the faces selected should all now be flat-shaded!
Also, remove whatever vertex splits you made after that. this is easily done by again tapping the space bar. but this time, type “remove doubles” into the box and hit ok. it should say up the top “removed xxx vertices” where xxx is the number of verts removed. (should be all the split ones…
)
If that sounds too hard for you, just send me your model, and I will fix it up for you!
I am someone who has often had to deal with shading problems like this before. One thing i have found also is that it often happens on low-poly meshes… 
EDIT: Also looked at your screens, that is weird that shader model 2 emulation would fix it as well… 
EDIT2: Actually, as Hippocoder pointed out below this post, doing the above splits verts anyway!
But if one is targeting a PC, it shouldn’t matter all that much. Plus, Unity only renders what is visible in the camera view at the time anyway, so unless there’s a really LONG corridor with 100 doors down the sides, one shouldn’t have a problem at all… 