Almost every dungeon has it's own set of items layed out. It is matter of which dungeon to pick to suit your current need. Mabi's incompetent drop table exists there for a reason.
But having said that, the general drop table is not very suited to smaller player base like us. It does get bit more problematic since GMs cannot change every single drop rates for each reward chests in the older content.
Back to the original question, I believe older content could be left as it is, or slight few tweaks to create a bridge for newer player base. What could be better is increase drop or create higher chance of reward for the new/upcoming contents since it simulates more party plays in comparison to the older ones.
I agree that there are some useful items in dungeons, specifically in the hard mode / advanced versions like Colin Plate Armor. However, I think in general that there aren't enough 'good' items available in dungeons to keep players running them compared to higher EXP / Gold rewards from shadow or theater missions.
I'm not advocating for a massive 'power creep' to rewards. Just enough to make it worth going back and replaying through the older dungeon content if people want to. New content is great and it's awesome that people are releasing it for free to this private server, but I also think older content should be kept relevant to a degree as well - otherwise it becomes kind of like the live version of Mabi where there's no reason to run older stuff, and the newer content always outclasses older content.
Thanks for the input.