Just a thought on economies as this seems germaine:
Back in the days of TAS, I forget the specific name of the article and the issue, there was a table of exchange rates (the differences between currencies on different planets and the Pound Ster....ahhh...Imperial Credit). There were some other articles on stock exchanges.
Why does that matter when you asked about trading (cargos I assume)?
Well, if you combine the articles on stock exchanges that can allow investments from PCs (local subsector or sector wide) with exchange rates, and then tie that to an interstellar trade system, then you've got just about all the financial and background story potential you could ask for. I don't think anyone has tried that - I did use exchange rates and that made some places bargains to grab cargo or good places to sell them. And everyone luuuuvs Imperial Credits. ;)
If you can meld these things and then tie them to a bit of computer code that would run a sector with fluctuations in trade, exchange and associated cargo fluctuations, that would be a very vibrant thing. I've thought of it, but I'd also want to include the ability to guide the program to deal with larger geopolitical events and random events in sectors and subsectors that would be impacting. Do that, and you've basically got a dynamic setting, rather than static.
Also, GT's trading rules seemed to be pretty darn good, but not easy to translate to a more normal Traveller 2D6 type system.
I do recall that someone built a massive spreadsheet for GT for (I think) the Spinward Marches and let GT's trade mechanics define where the trading mains would naturally form and the smaller routes (I think three levels). Somewhere, on an old computer, on an old drive, I have the map that comes out of that. It looks *a lot* different route-wise than the standard Spinward Marches map.
Ideally, one day, one of us will build some software that can be coupled to one of the great online maps or to an arbitrary sector map and use that and some decent algorithms factoring in nearby systems (J-1 to J-4 range, beyond that likely isn't economical) and UWPs and trade codes to come up with all trade routes (which would also tend, of necessity, to become part of any X-boat message) and then use that in conjunction with some exchange rates, stock exchanges, and random (or inserted) events to model changes over time and report those in a format a GM could use in game planning.
I guess the sandbox simulationist part of me is showing ;)
The problems you will find with many of the existing trade systems, and neat cargo systems (just for generating small speculative trade cargos), and even with basic premises for where you can trade and how much cargos should be worth are thus:
1) Static values that do not fluctuate, unlike the real world
2) Cargo values have a lot to do with markets which have a lot to do with supply across sectors and things like wars, piracy, etc. so they are more than just random variations
3) Different conditions on planets will have a huge impact on their interstellar trade. Places where an Imperial Credit is like a bar of gold relative to the local currency value (based on their economic development) will NOT do much interstellar trade even if there are a billion people on the planet. Similarly, religious views or changes of government could easily change the rules, so could pandemics (kind of close to home, just now!).
4) Stock speculation and runs on trading (if you are simulating a sector or subsector stock system) will have to either assume or build in possibilities of stock market manipulation and oscillations from computer trading, etc.
5) The cost of goods and staff, the relative hazard of particular areas of space, the ease and difficulty of securing cargos (for spec or as freight), the ease or difficulty of finding buyers, etc. are all impacted by conditions on each of the nearby systems and all of that means the costs should be more variable than the game presents and that means cargo purchase rates and sale rates and freight rates would all be more variable. And then again, with economic issues happening weeks away by jump, your traders are always making decisions based on out of date knowledge... and that has to be factored into their risk modelling and that further ups the costs and the prices they transport ship owners have to charge.
The way Traveller has always run trade has been an attempt to vastly simplify larger economic and political factors into a very dead simple (compared to the realities of what would be going on) system that lets Merchants and PCs on small ships have some fun with cargo. The various systems kinda work for that. But to get anything akin to a larger view, you have to bring in some of that complexity (maybe a lot).
I'd love to tackle this project, but most of my Traveller stuff is in storage offsite and I'm the caregiver for two elders, a wife getting through post-op recovery and not too mobile, and my 12 year old who has to learn to do distance education and hope that sorta works - which it frankly won't - to save her grade 7 year.
Maybe some year down the road.... I'd love to see a new release of Traveller Universe for modern OS and that and/or Travellermap combined with some economic and event engines and stock exchanges to really build a 'live' Traveller sector or two.
Tom B