you should have to balance production versus production capacity. to do that, you should be able to create, say, multiple markets, factories, and temples per city. these would be amenable to destruction in a siege. but, perhaps more importantly, if you develop, say, 10 temples and 1 market in a city, then you'd cripple your economy. if you have a city population of one million and you have only a single temple, people should get pissed and revolt. hence, you have to maintain a balance.
on the other hand, if you create too many markets, factories, etc., then you overheat your economy, and a depression ensues. that is, unless you're a theocracy, in which case your temples are tied to your economy.
your economy should also be tied to your neighbors', especially later in the game. if you go to war with your neighbors, your economy should take a big hit. if you want to go to war, you should have to borrow, but it should cause a mild depression after the war. later in the game, wars should be painful to execute, just like in the real world. if you're going to war, you better win big.
which leads to politics. a large, powerful neighbor should be able to exact economic, military, and diplomatic demands on their neighbors, with the threat of economic sanctions and war. for instance, if you're germany living next to russia, and they decide that they don't like your alliance with another nation, they should be able to create a trade embargo that's painful. they should also be able to exert some degree of control over your policies.
which leads to winning the game. in the 20th century, the united states clearly won. in the 21st century, likely china and/or india will be seen as the winners. in the 18th century, the united kingdom could be considered the big winners of that century. while an all-out domination victory would be awesome, as time progresses, it's increasingly impossible to execute in the real world. it's highly unlikely that chinese troops will ever end up occupying the streets of berlin. so how do you win?
1. you survive. the game should make survival much more difficult, as you can get assimilated or controlled by other civilizations. a technological misstep, or improper army sizing should effectively end your civilization, depending on your neighbors.
2. you implement a massive effort to control other civilizations. if your economic fortunes are intertwined with your neighbors', and they can't make a move without bringing down their economy, that's a huge win. think japan in the modern era. it has no military, but it's the world's 3rd or 4th largest economy (depending on whether you count the european union as a single economy). if japan stopped producing, it'd cripple some economies. in the game, such a civilization could win at least a partial economic victory, though they don't have the massive clout to pull off what i'd consider a win in civilization.
another way to effect a victory in this manner would be to exert cultural control over your neighbors. create parcels of culture. nike, coca cola, levi's, music, and movies. one of these alone shouldn't be enough to be considered a win. however, a cultural win combined with an economic one could potentially be a win.
3. you pull a stalin or hitler, only actually win. if you control certain regions of the world (the underlying military philosophy used by the germans, to limited success, because it discounted aerial power), then you should win. for instance, stalin controlled a significant portion of the world after world war 2, but in civilization, i'd still consider his civilization as losing to the americans, by virtue of the u.s.'s cultural and economic prowess.
4. i like the technology victory option, but getting out of the solar system shouldn't be the ultimate goal. other countries should have to rely on your technological advancement for theirs, and the more they adopt your technology, the more points you get here. for instance, a country like france may not like having to adopt the internet, because it erodes their cultural hegemony, but they should have no choice.
in summary, what i'm arguing for isn't a single type of victory. victory shouldn't be that easy. it should take a preponderance of cultural, diplomatic, technological, and military superiority to count as a win. unless, of course, you pull a stalin and actually pull it off.