Not wishing to argue for it's own sake here (believe it or not
) but I think such random variances can be imagined to cover all kinds of stuff - once said 'stuff' all gets pinned down then we lose something in my opinion.
For example: If I buy food for 2 credits then can I expect it to be the good stuff? Maybe I buy it for 6 credits and the next station only offers me 2 for it, maybe it's not the quality, they just don't eat it here. If I bought from multiple sources then perhaps they are only offering me the average price.
All true, but it's still all just "Food". Food from the system next door is the same as Food from halfway across the galaxy, and it's all in one narrow price band. Computers from low-tech planet A, next door, earn the same as Computers from high-tech planet B, from way over there. It's part of the ultra-basic trading system. As I said, it's a miracle of programming for its age, but …
In name, yes, it's still just food but but by 'quality' I mean is it doughnuts or caviar? Caviar costs more but in many circumstances the demand would be far less... (to be fair, caviar could be classed along with luxuries)...
Anyway, I'd agree about price range for the most part and your 'do away with it all' suggestion does avoid the problem of needing potentially tables and tables of goods rather than just the one we have at present.
What trading perhaps should have that delivery contracts don't is much less predictable rewards. The profit margin at present is rather predictable; it probably needed to be in elite but that is perhaps not the case with oolite. Does somewhere beset by occasional civil war offer higher prices for firearms ocassionally
? Does a tedious planet offer more for narcotics and luxuries? Potentially interesting but also more complicated.
Computers and furs are the big sellers at present from any industrial or agricultural (respectively) that sells them.
What if for each industrial the big profit was to be had from a random industrial product, e.g. computers are cheap at industrial A but expensive at industrial B, whilst machinery is cheap at industrial B but expensive at industrial A. So the biggest profit items will at least vary between systems.
Some industrial produce items: machinery; computers; firearms
Some agricultural produce items: liquor/wines; furs; narcotics
Even with a simple set of items like the above, imagine if each planet offered a particularly cheap price for only one of the above (e.g. an industrial selling machinery cheaply) and was only willing to pay significantly above the odds for one other (e.g. the same industrial offering a high price for furs).
I've got a good price on the machinery here but will it be what they really need at the agricultural I'm headed to? If not I'll still make a profit but if it's the one they really want then I'll score big!
Trading would still be safe and simple but much less predictable and with greater variety - you might actually need to read the price list besides checking out the precious metals and gem-stones!