In addition to using the OPEN MATTE versions, maybe some few improvements from Doctor M’s The Enhanced ABC Cut could be used?
Now, a few more random ideas, though I have no idea how well this could work
- Consistancy with the use of Polyjuice Potion. It should either always change the voice, or always keep the voice.
- In Chamber of Secrets, the diary memories had a certain color tint to it. Maybe apply it to the Pensieve memory scenes in the other movies, for a consistant look?
Overall, making magic spells and effects consistant is something that can really improve the experience.