The upgrades you notice every single day
A finish change is what visitors see. Hardware and storage is what you feel, several times a day, for years. Reaching into the back of a deep base cabinet on your knees with a flashlight is a design failure that no amount of new paint fixes. A pull-out shelf does.
Best done while the doors are already off
Hinges, runners and internal storage are all far easier to fit when the fronts have been removed for finishing anyway. Bundling this with a painting, refinishing or refacing project typically saves a meaningful amount against having it done as a standalone visit later, because the access work is already paid for.
What actually gets used
After thousands of Ontario kitchens, the pattern is consistent. Pull-out shelves in base cabinets are the single most appreciated upgrade. Soft-close hinges come second, mostly because a household with children stops hearing slammed doors. Deep drawer dividers get used constantly. Corner carousels are useful but only where the corner cabinet is genuinely dead space. Decorative internal accessories are the ones most likely to be regretted.