3D Output
Suggest you use the open source Meshlab program for editing, converting between 3D formats and point clouds.
I have done 3D crystal engraving using a sub-sampled point cloud. This is particularly effective when lit by variable LED's but you will be limited by the available crystal sizes. The laser creates micro-cracks in the crystal at each data point. You have to experiment with the density of point cloud, scale and offset it to fit inside your chosen crystal block size using (0,0,0) for one corner or as per your engraver's requirements.
For 3D plastic output, find someone familiar with it who has a machine and work with them. The main problems are small passages and having to use lots of cutaway supports. You can subset the model based upon elevation and then 3D print each elevation range using a different colour plastic - helps with model visualisation and display.
You can try fused powder deposition but this will give a solid form and small passages will be fragile.
If you want realistic colour from 3D photogrammetry models then this is possible by subsetting the 3D model and printing out small sections with no overhangs plus added joints to aid assembly but the results are very time consuming and not the best. Might be useful for a cutaway passage/chamber display.