What I use MeshLab for is in the following order:
1) Filter -> Cleaning and Repairing -> Remove Duplicate Vertices
2) Filter -> Cleaning and Repairing -> Remove Duplicate Faces
3 Can't figure out / Ignore) Filter -> Cleaning and Repairing -> Merge Close Vertices
4 Optional) Filter -> Remeshing, Simplification, and Reconstruction -> Simplification: Quadric Edge Collapse Decimation
The last option is to reduce geometry faces. Be sure to check the checkboxes for first three options in the window prompt. This actually works pretty well. It will obviously change the look the more you reduce but pretty decent if you need it.
When you do the first two steps, and export, you'll have a dramatically smaller file, and the change in look IMO looks better and seems to remove junk data.