I have no hands on experience with the LS-30 but I do have with the LS-40.
After strugling with flatbad scanners and adaptors, I decided to get a desktop scanner. The LS-30 was out of scope after reading the specs. I don't remember what was the reason of ruling out the LS30, but I quickly concluded that for my purposes three are only three possible Nikon candidates: LS2000, LS4000 and LS40.
Since the LS2000 is no longer manufactured, plus it would need a SCSI controller and costs nearly the same as the LS40, I went for the LS40; I am satisfied with it. Indeed the pro version (LS4000) has more features and accessories, but I am happy witht he image quality of the LS40. I would consider the LS40.