Next, my current cargo and missions - remember that this is a Planet Express, a small lightly armed ship, with a lot of cargo space taken up by passenger accommodation:
Small, lightly armed, but ridiculously fast
compared with the core game ships.
The balancing is supposed to be "you drop into a dangerous bottleneck en route, and with that many high-risk parcels on board about fifteen separate groups of assassins try to claim the kill", to either make you pay a significant repair bill, take a detour which reduces the profit/jump or the number of simultaneous contracts, or give up and do something safer. If you can go at 0.55LM while the fastest assassin in an Asp goes at 0.4, then they stop being the threat they're supposed to be. (Gal 8 is also a bit short on really dangerous bottlenecks - try taking contracts into or out of the top left corner of Gal 2 if you want more of a challenge...)
The precious metals contracts are indeed excessively profitable - note that the Rain, Tioned and Orbira contracts individually each pay more than the entire parcels+passenger set you have combined (of course that's the gross rather than net payout, but still...). There's a bit of balancing in that you have 6 TC of precious metal canisters in your hold, so if you do get hit through your shields you can end up losing 40/80,000 credits in a single shot - but again, with that speed, why would you ever lose your shields?
Switeck did put together a mod for the cargo contracts to rebalance them, which might be worth a try. Unlike passenger and parcel I haven't changed the cargo contracts significantly from the 1.76 version, because I can't work out what's needed there. (The forums have successfully talked me out
of a few possible ideas, but not into any)
All that said ... by the time you have the rep and in the case of cargo contracts deposit money to take on that many profitable contracts, you also almost certainly have no real use for money other than the accumulation of further money anyway. As an early-game activity they're generally much less effective ways to earn money than conventional trading or the bounty hunting/scavenging approach.