The difference is all in your calibration, the only reason the VHS ones look more '3D' is that the levels are closer to what they should be. You really need to calibrate your SVIDEO capture - can your camera create colourbars?
When calibrated the Hi8 pics look much more '3D' and have better colours and far more detail than the VHS pics, you can tell just by looking at them as is.

Also the missing 'dots' on the VHS copy are just missing detail, it is obvious from those pictures that the VHS copies have a *severe* detail loss compared to the Hi8 ones, if you blurred the crap out of the Hi8 captures to make them equal then the dots will disappear from the Hi-8 pictures as well (along with all the detail just like the VHS shots posted)