as long as it does not modify research (research should be seperate from gold/economy imo), then I am fine with a wealth score.

As far as options when taking a city go ... Occupy, Sack n Capture, Exterminate and Capture, Pillage and Leave, and Raze.

Pillage and Leave, or Sack n Capture, would increase coffers (and wealth) the most, while Exterminate (n capture) and Raze would add Dread/Notoriousness/Evil-ness to your general, army, or nation as a whole, and would serve as a negative modifier for friendly nations, but a fear/respect feature, where people would become less likely to declare war against you (unless on some religious holy mission)

Yeah, I would like to see some other factor involved with city strength other than population number.  Wealth opens up some other interesting city varieties too.  Think of a desert, oasis city between two merchant empires.  It may not have a an exceptionally high population, but would have very high wealth.

Not necessarily. A wealth score wouldn't be a major overhaul of the system, really. Personally I like the idea of trade and certain buildings, for example, modifying the gold/population of a given settlement. Although I suppose whether these things modified gold/population or just added additional income would have about the same effect. But I guess my point is: I would like to see certain types of buildings and trade increase income.

I'm still hoping for trade to be meaningful in this game, but it's seeming less and less likely...

Right this is what I'm thinking, especially on the trade issue.  On the topic of wealth, I was primarily petitioning for not only what the empire has and is gaining in taxes, but also the wealth of the people which is being taxed.  I think this could have some vivid effects in regard to making trade relevant.  I mean, it was okay in Galactic Civs that you had trade routes, but those trade routes didn't actually do anything beyond give you some extra cash.  I think trade in certain resources might especially be interesting, but you'd have to keep it relatively simple, otherwise it would become too much management. 

What might work is if a kingdom has a certain "commodity strength" score on the diplomacy screen which represents the total sum of special goods that your kingdom expoits.  This would be accompanied by an "effective commodity strength" which is posted next to the portrait of each kingdom's leader: this represents the bulk of goods that you have that another kingdom actually needs.  For instance, you might exploit a "Diamond Mine" which gives your civilization, amongst other things, 100 commodity strength toward Kingdoms without Diamonds.  A "Run of Wild Game" might give your civilization 20 commodity strength (exotic pelts) toward such kingdoms too.  If you sit on these commodities, wealth will grow slowly from them, but if you open up trade with the right Kingdom, wealth grows much, much faster (and that wealth subsequently is added to tax revenues).  When trade has been established, your total strength will likely fall across the board as the supply of certain goods are exhausted.  If you have a high commodity strength with Kingdom B and they have a high score with you, you develop a very lucrative trading arrangement but a lot of your commodity strength is used up because you are meeting a lot of each other's product demand.  Also, you can never trade with a player more than the lowest of either player's effective commodity strengths (for instance if you simply don't have any more diamonds to trade for their pelts.)  

If you don't want to use up all of your trading strength with a given opponent, you can always set standards by which only a certain amount of your strength can be exhausted.

I think trade-based wealth and/or prestige would be an incredible addition, especially if it is done on a per-city basis. It'd open up a whole new potential focus for cities, and it would go a huge way towards making location important. For example, if there's relatively barren area of land (no resources to speak of, not particularly defensible, etc) - there is pretty much no reason anyone would ever build a city there. As it stands resources and perhaps defensibility are the only factors that affect city placement decisions. However, if you notice that there's lots of trade passing through this barren region, perhaps you will want to start a city there - it's contribution to your nation would be trade-based wealth and prestige. Trading hubs, both in reality and fiction, have always tended to be some of the wealthiest and most thriving cities, despite a dearth of actual resources of its own. It's importance is solely due to its convenient central location, where people from all around can meet in a single location to carry out all their trading; or even as just a stop along a longer trade route. Most of the major ancient cities in the Middle East and Asia Minor, for example, existed almost solely because of trade.

It's something that's realistic and, IMO, would be extremely fun!