It is a 2 sided sword. If it happen to a weak Civ then it gets weaker but if it happen to the #1 Civ then it gives a chance for the other Civs to go back in the game.

In my opinion, when two or more cities (same nation) start building the same Wonders, the rules must be that one is also the city where the Wonder will be built, the others simply support (no more by CIV Caravan or SMAC supply units) the building, introducing some % of shields lost for inefficiency and transporting costs.

This will avoid the trick to start same Wonders in two or more cities, just for switching when new Wonder become available by tech research or tech trade.

I'm not sure about the problem of losing the wonder rush: how can I do with an almost finished Pyramid? Considering how often old Wonders become used as deposit of raw materials (stones and metal) for other building, I simply suggest they slowly become consumed adding resources to the next buildings in the same city at half the rate of shields, for the same building turns (you will end losting 50% resources).

Ok, it's really a draft formula, please correct it as you like. The concept is I can reuse something, but not the workhours spent (they are fully lost), and taking the time to recycle some parts.

If you think this only work for stones and the like, please consider how often also ideas and tools can be used in a different project.

Well, at least with Santa Klaus I used to write down my wished gifts on a letter!

Back serius, I think we have more than enough surprise with Civ 2 hut discovery, or SMAC pod race.