I don't see them as being that difficult (I've done plenty, back since 1.1 when there were far fewer in-game hints and tools for it) and they certainly don't require the use of out-of-game tools.
1) See mission
2) Find economy type that sells the goods by one of:
a) Common sense "Fish" -> "Agricultural"
b) Experience and knowledge as a trader
c) Checking the commodity market info for the good and seeing what type of economy produces it
d) Checking the commodity market info for the good and seeing which specific systems it's normally imported from
3) Set map filters to Economy mode. Maybe check BGS states just in case.
4) Decide whether this fits with other missions, etc.
5) Take mission, fly to appropriate system, buy goods, bring them back, profit.
I mean, certainly, they require slightly more thought than the average cargo mission (and it does get slightly harder on the rare occasions the requested good isn't one the station has a standing demand for, though that still leaves plenty of options) - but all the information needed to do one is available in game. Easily so, now we have map filters, import/export descriptions on the market screen, etc.
As regards efficiency ... the trick is to blend them with other activities, and to make use of local knowledge:
- courier mission taking you to an Industrial system? See if there's some "Fetch <Industrial Cargo>" missions on the board for your return trip.
- heading to a Refinery that often has this sort of mission? Buy 20 tonnes of HE Suits (or whatever it is the missions tend to be for) before you go: if the mission shows up you'll have the cargo and can make several thousand credits per tonne on it.
- heading to a system in Famine? Buy a range of food types rather than just the single most profitable one, to increase the chances of hitting one of these missions for massive profits.
They could be made as a zero-thought variation on the "deliver cargo" missions - "fly to station X and you'll be given the mission-specific cargo to bring back here" - but having them be a little more complex is I think good