Yeah, you definitely have to look at values on the Income/Expenditures screen and not the slider positions. For instance, I went from around 3000 income to around 3400 when I switched to Star Democracy earlier today, but the net income dropped to a big negative number because my ability to spend increased as well, so the current slider position had me spending far more than I was before.
This can happen in lots of areas. For instance, if you have a turn where you add a lot of production modules to starbases (especially big ones, like +25% phase 3 and such), you'll often have to lower your expenses because your improved production now makes your current slider setting spend far more than it did before.
If you don't raise your production through the various means in GalCiv (better government, production buildings, production starbase modules, etc.) but do raise your economy then you can reach the point where you can't spend enough money vs. your income (i.e. expenditures are at 100% but you still make money). Not only do these improvements add to your power, they also give you room to use that power to its fullest.
There is a certain Zen feeling to the GalCiv economy, once you get it you get it, until then it's 'the sound of one hand clapping'.