Washed out colour is common in manually scanned manga from physical copies (Evident from the imperfect stitching on the 2 pages spread).
Instead of directly using contrast adjustment, I'd suggest atleast using the levelling function or if possible, curve adjustment.
https://www.insidescanlation.com/etc/the-idiots-guide-to-editing-manga/guide/cleaning/level.html
Looks like your current RAW is pre-processed already and requires only little additional work. Should dust and moire crop up in the future, QSS has an incredible collection of guides for dealing with old-school physical scans.
https://quicksandscans.wordpress.com/dusting/
https://quicksandscans.wordpress.com/resources/