Luddite said:

I get the impression that many of the worlds are so specialized that they are not self-sufficient, i.e. hive worlds can't produce enough food for the populace and agro worlds have little industry.  As such trade in necessities is what drives the various economies.  The Imperium could largely be based on a barter system.  Perhaps there are even 'warehouse worlds' where surpluses are stored and sent where needed, almost a socialist economic system.  There still are profits to be made but by comparison, I don't see a large luxury/leisure item market.

Rashid ad Din Sinan said:

Warehouse worlds!

Excellent!!  I love that idea.  It reminds me of the EEC 'butter mountains' and 'wine lakes' that built up.

I also like a more 'socialist' model of economy.  It fits quite well with my own idea that the economy of the Imperium, founded on the value of food and water to sustain human life.  Of course, even within the most ardent 'socialist' society on earth (China), capitalism and the pursuit of wealth and and always has been ingrained in the populace so perhaps a look at the Chinese model might be a good step?

Different races would put emphasis on certain substances....

Imperium - promethium, adamantium, psionic blockers. The novel "Star of Damocles" describes the refilling process for warp drives, complete with dissolving workers...awful. Whatever the stuff is....the hazards make it probably the most dangerous and expensive imperial substance.

Eldar - won´t care as the fabricate everything from thin air...but a large collection of way stones would buy a lot of favours

Orks - tooth...and scrap. But they won´t barter for it. Shady places with natural moisture ?

Tau - metal alloys. Aside from that, they will generously give if offered "furthering the greater good". You can buy everything from the tau with honesty and goodwill.

Necrons - Won´t trade. Ever. And are not disclosing what their production cycle is based on. Probably something even better than "thin air".

Chaos in any form - as diverse as their belief, everything imaginable. Will also malevolently barter for grief, sadness, lust, massive bloodshed, etc.

Luddite said:

It would cut down on the risks of warp travel.  Make psyker 'ordering' easier by having standard symbols & amounts, kind of like having the picture of the item at the register at Mikkey D's or '#1 soup' at the Chinese restaraunt.  Also allows for interesting plot hooks for pirates, marauders or espionage for poisoning food supplies or destroying war materials.

Luddite said:

And the wealth would be who controls these worlds and, as in supermarkets, the cost of shelf space for specialty items.  Might also be located near military bases and spacedocks considering the amount of traffic such planets would have.

It also adds some incentive to go looking for planets in 'the dark', empty space between shipping lanes, to speed up transit where 'less warp the better'.

Luddite said:

At the lowest level of the Imperial social order, citizens, through the constant teachings of the Administratum, know that from birth they are property of the Imperium. An entire planet tithing varries as to what they have to give. An agri planet provides food, while forge worlds build the engines of war. The average citizen can only give themselves. Only through aligning with the 'right' offices and political bodies can they every hope to advance their own lot. Most will forvever be power poor, live and die a few kilometers from the place where they were born. Only those citizens who manage to show enough fellowship (to use a game term) can gain power over their fellows.

This power can come in the form of fear, intimidation, admiration, or favour, to name a few. The power comes, when another citizen comes to look upon those with power as necessary for their own survival within the Imperium. Political favours can be more valuable than local planetary currency. Wtih the right political connections, as any noble knows, it matters little how much much monetary wealth is held.

Of course, there is the arguement that might makes right, and those with enough might can certainly take what they want. But if the most powerful trading house feels it owes more to a puritan than a radical, there is little a radical could offer to procure, for example, use of a ship. The radical might have to think about destroying the house ( time consuming), intimidation (could backfire if puritan rival is called in to defend), or offering a little piece of that political currency (could be information, future favour, etc).

Well, at least that's how I see the value of political power.