I think that something IS gained by something even as abstract as 'Raw' and 'Refined' shields (though perhaps Raw resources should be defined by a symbol like a saw log or a lump of ore or something). They can help to define how much of your production are in the form of raw materials-and how much is in the form of your 'human-resources'. This might lead to a situation where a city produces large amounts of timber and stone, but where they lack the man-power to refine it effectively (or suffer from too much crime/corruption). Thus, they send it to a large industrialised city for refining.
Of course, another major difference that can result from even an abstract system is that raw resources are worth NOTHING within the city they are generated in, and are worth only a small amount in domestic and international trade. Refined resources, OTOH, are worth a great deal more.
A compromise position could be this: raw resources are 'abstract' when they are within a city (i.e. stone, wood and metals can be equally 'refined' for use in production). However, where the TYPE of resource becomes important is in TRADE. For instance, lets say you have a city thats SURROUNDED by forests. Over 80% of the 'raw' resources it would send would be either 'Timber' or 'Forest Products'. Thus, the trade screen would show your 'shields' divided up according to 'where' they came from. Then, how much they are worth would depend on how short other cities or nations are of that specific resource.
Lets see if I can come up with an example:
Lets say you have city A: In its city radius are 2 forested squares, a hill square, a mountain square and a plains square. In all, these produce 15 'raw material' shields, which appear in a seperate box. At the bottom of this box, it tells you what % of these shields are of each resource type (Minerals, Stone/Clay/Rare Earth, Timber, Natural Fibres, Hydrocarbons etc.) In the case of this city, around 30% would be Timber, 40% might be natural fibres, and the remaining 30% might be Stone/Clay.
Now, lets say that your city had NO other sources of Stone/Clay, then any stone/clay that left their city would make more money than, say, its timber-unless timber was non-existent too! How much of each resource ends up traded would depend on the %'s I mentioned above. So, if you sent 10 of your raw shields to the central trade area, then 3 of them would end up in the timber queue, 4 would end up in natural fibres, and 3 would end up in stone clay.
The same 'supply/demand' equation would also apply to international trade though, once it ended up back in a city's 'raw resource' box, it wouldn't make much difference anymore.
Another thought I had was that especially rare food and raw resources could act as 'pseudo-luxuries', in that they boost a city's happiness by a certain % for a few turns after they first arrive-if that makes sense.
On a final note, I think that if you have specific raw resources, the best thing to do is to keep it simple and broad. i.e. don't indicate EVERY single mineral-just leave it at MINERALS. Same with Timber, natural fibres, hydrocarbons etc.
Anyway, sorry for the VERY long post, and I hope that it all makes sense.
Yours,
Aussie_Lurker.