Have you ever tried?

I did. I had the same opinion as you do, and I tried to do those metal-pick ups which wasn't that hard, especially not on the second planet. Anyways, after fiveteen minutes I collected around 100-130 and sold them all, but didn't even earn 1.000 Gralats. So, this was way too boring and hard in the long run, I tried to kill those aliens and PK/base. It was pretty fun the firdt half hour and I earned a few $10's but then having the starter gun and no money to buy any other gun killed the fun there aswell. After a few days of tryharding for some minutes I finally bought a second gun (the Metallic Riffle) and gave it a second try. Ten minutes after, I decided to not try again..

There are enough ways to earn Gralats, yes. But the way how you get those seems very boring and hard in the long run and could have some little changed which add fun to those..