Nono, I love the buying mechanic.
I'm just saying that you can balance certain "roles" by adjusting the attributes of the weapons, items and tools. For example, if a player wanted to be a frontline soldier, they could carry a rifle/SMG and a sidearm, as well as grenades and perhaps one "utility" item, such as a medkit or a light digger. However, if someone wanted to focus their attention on mining, they could buy the heavy digger, but could then only carry a sidearm and perhaps a few grenades or something.
Also, gold carrying capacity would increase the larger the model of digger that was bought, but there would be tradeoffs in what other items a player could carry. If you're running around with the large digger, you can get gold like crazy, but you can't carry many weapons.
As well, I was thinking about the gold-collecting mechanic. While the idea of instant gold to funds transfer simplifies things, there's something fun (to me) about flying the rockets back into space packed full of gold. Instead of loading up the big delivery rockets, maybe an idea you could implement is miniature "gold delivery" rockets that a player can launch and control directly from their mining site.
The tradeoff would be that these rockets are slow and can be shot down, spreading gold dust all over the crash area. Then, part of the mining strategy would be not only digging tunnels easily accessible by your team, but also digging missile silos from which to launch your resources into space. Using the deformable terrain, enemy forces could attempt to cave in your silos and prevent your resources from reaching the atmosphere.
Just some ideas I'm playing with.
I like my idea with the light - heavy soldiers/workers classes.
