The difference between Mackie preamps isn't going to be "night vs. day".
The newer designs are slightly better.
If you're wanting to experience a major improvement from your mic preamp, you'll want to go with a higher-end outboard model.
I picked up a Neve Portico-II a year or two back.
One of the best gear investments I've made. Literally everything sounds better running thru it.
It's like getting a gear upgrade across all your mics/instruments.
The downside (of course), is cost.
IMO, All onboard preamps are slight variations of "pretty decent" (not amazing, not horrible).
You won't find a lot of color/personality with any of them.
In the OP's scenario, the A/D converters are currently in-the-box.
A new audio interface (converters outside-the-box) would yield lower noise-floor.
You may not notice the difference across a single track, but take that 6-8dB improvement (exact amount depends on the audio interface) multiplied across 24+ tracks... and it starts to add up. It's like peeling a veil of noise away from the project.