1. Replace all computer rendered LCARS screens, that look very pixely, with new antialiased graphics. The screen resolution of LCARS looks very dated - they often remind me of screens rendered by old 386 computers.
2. In the conference room you would sometimes see the narcelles of the 1701-D instead of the open space. So some shots should include the narcelles now.
3. Use high definition animated computer graphics for planet surfaces instead of the bad soundstage buildings. You immediatly know that they aren't "on location" but on a built set.
4. Make the ship more crowded by adding filmed persons against green screen into corridors or 10-forward.
5. Fit the color of the footage (red-ish) of seasons 1 and 2 to the later seasons.