Edit exported 3D files, is there an extension that assists with this?

SketchUp Pro
,
5

Generally be sure to read:

SketchUp User Guide:

And take note that:

During export, you may need to open the “Options…” sub-dialog from the file export browser dialog. The button is usually located somewhere on the lower right of the file browser dialog.

This is SketchUp 2015 (and earlier,) which did not yet use the MS Common Dialogs v6:

The “Options…” button is in the extreme lower right corner.

This is SketchUp 2016+ (Windows v6+ [Vista] & higher) with the file browse panes collapsed:

The “Options…” button is just to the right of the “Export” button.

This may be due to not using SketchUp’s inferencing system patiently enough. (You often need to wait a half second for the inferencing tooltip to popup before clicking.)

Make sure you are using SketchUp’s tool and inferencing correctly when modeling:

SketchUp User Guide:

This is often the extra 3D edges caused by the triangulation of SketchUp surfaces into export meshes. SketchUp internally can have surfaces made up of triangles, quads, and even faces when a higher count of vertices. But most import & export functions of most applications expect surface meshes of only triangles. So any quads (or faces with 4 or more vertices,) are broken up into triangles during the export process.

Also, in SketchUp, the viewport rendering can be set to soften and smooth these surface edges, so that the view looks smooth. You can see these “softened” edges if you check the menu item:
View > Hidden Geometry

So partly, some of these “extra lines” in the CAD export are not really “extra” at all. They are there inside SketchUp, but just “softened” by the SketchUp viewport. Others are the result of triangulation.

Not sure what this is as we cannot see the model as it is in CAD. If you have “Color By Layer” on in CAD, and there are lines on different layers, ie, SketchUp may have exported groups or components to there own individual layers during export.

This is definitely the result of not opening the “Options…” sub-dialog during the import, and setting the scale.