I agree with the OP, Credits are too easy to earn. Progress in the game is much too fast. As a consequence they had to implement an alternative currency (my beloved 'materials').
IMHO materials should be also sold by material traders for a lot of credits, and it should be not sure if a higher level mat (G4,G5) is available at a certain trader. And they should be expensive. Nothing else should be changed. Maybe the material traders should also buy mats, but at very low prices. This way everybody who enjoys the material search can continue to do it, and others like me can buy the materials.
Materials are an alternative currency as it is now, you cannot buy them, and you do not loose them if your ship is destroyed. This is quite illogical but necessary. Changes would not hurt here...
Also flying (not owning!) a huge ship should be much more expensive! If somebody has (exaggerated) billions of credits and 3 Anacondas, and at this time flies for some reason a Viper or an Eagle, he would pay small sums only, but as soon as he flies the Anaconda, this would be much higher. This is actually implemented via 'Wear and Tear', Advanced Maintenance - it is only much too cheap. In IRL - look up what a Heli hour costs, subtract pilots fee and fuel - what remains are the maintenance costs, and they are quite high. This too would be a money sink, and it would it make much harder to own a huge ship after one week.
Also, storing ships should be prized. Stuffing stations with armadas of large ships for free?! Hello?!