It's actually just a passive income system with an exponential formula that increases with time. There's other ways to get income but this is where 95% of your minerals come from. It's dull and lacks depth.
I actually have a kinda good idea for this then.
Seeing as how there are two types of resources, minerals and vespene, what you can do is this.
For each control point you have, you gain more minerals, but you gain less vespene in exchange.
Heres the rationale:
1). Minerals make you able to buy higher tier items. Over the long term of the game, this will mean you eventually win because you have a better income if you hold onto more of the control points.
2). On the flip side, Vespene should be more valuable for the short term, like giving all the bio a stimpack like buff for a short time, or dropping down units that are good at pushing the enemy bio back. In this way, if one team loses the middle, they haven't completely lost the game, as they have an opportunity to push the lanes back and retake the middle.
3.) This still leads the game towards an end, because holding the middle becomes more and more valuable the longer you hold it. If one team is working together and keeping the lanes from pushing, then they will eventually win the game, as it should be. But because you gain more vespene the less nodes you have, it isn't (as I am drawing it is now via previous posts in this thread) that whoever gets the early advantage always wins.
EDIT: To clarify, the minerals will still ramp up slowly over time as it is currently, just the ramp up will scale based on how many nodes are controlled.
Well on the idea of the income system, I haven't played the map as I am in the US, but I am assuming that your system uses the dota esque idea where when you kill an enemy tank, the owner of the killing unit gets all the income.
An idea is to use a function which gives the owner of the killing unit some higher percentage of the kill reward minerals, maybe 40%, and then splits the other 60% among the remaining 4 players (15% for each in this case). If you look at how DotA worked, the "Carry" heroes always got more gold in the end than the support ones, but that was the intent. You have support to give your best mech all the tools it needs to demolish the other team (slowing, disabling, healing, etc. etc.) so in this sense, you'd still be giving the killing unit a benefit over the other players, but you are also still distributing the minerals around the team, so they don't fall too far behind.