Here’s the bottom line: there’s no such thing as “upgrades”. There are only modifications/setup/repairs. Any modification you make will give up something to get more of something else. There is no backing up the truckload of goodness for a fillup.
Before making any modification or even setup change, it’s best to have some idea of how you want it to be different. This is even true for setup. For example, dialing in the action height depends on what you are trying to accomplish. Despite what you may read in forums, ultra low action is not always best.
Of course, sometimes you just want to see what happens. Some changes can have a big effect without spending a dime. If you measure carefully and take notes beforehand (and think it over before cutting anything), you can often reverse what you did if it did not turn out like you expected.
Exactly. Wise advices @sgarnett.
That said, I think that going from this :


To that :


Over the :
modifications/setup/repairs
Can be nonetheless considered as an upgrade in itself...
A+!