Don't get the "just don't do the side quests, no one is forcing you" people. So you would only do them if you were forced to? Why play the game at all then? No one is forcing you.
That nonsense aside, after a cursory examination of the game's files, it seems all of the quests are stored in xml in data\quests folder. But they only have an "experience level" and "experience weight" values, the former being (mostly?) single digit numbers. So i guess they should be multiplied by something in order to get total experience, while the latter obviously point to how much of the experience you get in each quests stage. So after some testing to determine the multipliers i guess its possible to determine total maximum quest experience by parsing all these files.
The exp tables themselves seem to be somewhere in unity assets or dll's, so some unity thingie or visual studio would be needed to modify them. Hoped they would be in xml as well.