As to the VFX in ST3 I this is the film where the effects go wholly ILM style and it shows. In TWOK there's still a nod to the style of TMP in terms of the lighting on the Enterprise
(notably in the sneak attack sequence), but by this movie they've fully dulled down the Enterprise
and are shooting it like Star Wars model. Minus Probert and Mike Minor we start getting starships minus key features like warp nacelles, etc. There's some really sloppy slapdash work in the film, like the explosion of the E's bridge, which is clearly sitting on a flat table and not a saucer, and the closeup of the torpedo launcher wherein you can see they superimposed a shot of the saucer over the partial model and completely misaligned it.