This may be the case of the wrong tool for the job. That is, Inkscape might not be able to do this (yet). Or it might be best suited to another tool, such as a 3D program. (No, I have not tried Blender or any other 3D program.)

While I was trying to learn a certain other vector graphics program and looking for an easier way to produce a 3D look from a 2D object, without creating extra paths that might or might not look realistic -- I tried the 3D rotation and extrusion filter this certain other vector graphics program has. Oh wow, that was kind of fun! The results looked beautiful -- for objects that the filter was suited to handle. For others, not so much. But when it got it right (or when I figured out how to get the results I wanted) the results were quite nice.

Only -- The file sizes! A very simple 2D slice, rotated into 3D to produce an object, in these cases, a bottle or a dish or bowl, created very large source files. Then if you were foolhardy enough to export to any vector format (SVG, for example) instead of PNG or JPEG, well, you were going to get a file that was truly stupendously large. (The salt/pepper shaker example I produced was several *Megabytes* from a slice for the glass bottle, the metal cap, and the only complexity, grooves that should've been holes in the shaker top.)

I thought "flattening" the image would work, by reducing the 3D project back down to the 2D surface seen from the viewing angle. Nope. Whatever flattening it did had no great affect on the file size or the 3D extruded result. (Why it couldn't save the original slices, which were still there, and the 3D rotation parameters, instead of whatever amount of paths/polygons....)

Well, needless to say, I did not feel inclined to use a vector drawing that many megabytes in size, since the output and other requirements would have been wasteful and without any real value, visually or time/space production or output-wise.

But it left me wondering how it might be possible to create fairly simple 2D slices to make 3D rotated or extruded objects, and then have Inkscape save those source parameters somewhere, but then output to a final file either the fully realized 3D object, or else (what I was after for that drawing) the 3D result reduced back down to the 2D representation seen from the given angle.

Quite possibly, the answer is that I'd have to learn a 3D program like Blender. :-/

But I thought it couldn't hurt (much) to ask here and see what turns up. Or around, as the case may be.

hello,
While you are waiting an answer from a super techy person with way more knowledge than I have, let me let you know what I do in this case.
I need fairly large sizes (to sell), so once I've completed my drawing entirely, group everything together (hint, if you want or need to keep items on separate layers then duplicate a copy at this stage and move it to a new layer, hiding the other layers, or simply make a new svg file). Anyway, then I use ctrl + arrow and size everything down to around 25% (in the bottom right-hand corner shows the size). Then to to the Edit Properties Menu and click on the resize button.
Now, (and this is what really counts, not so much all that garble I just wrote), click on File -export bitmap, then I usually export the entire File, and change the DPI pixels, I usually aim for exporting between 200 - 300 dpi. that will keep the files fairly normal.
hope this will give you something to play with until someone else comes on that has better answer for you.