I don't think Scientific Leaders are a problem, rushing wonders or not. Then again I figure I can always go capture the city that has the wonder in it if needed.
Truth be told, I usually don't even start getting wonders until the second half of the middle ages or later anyway, so I am sure that is one reason why the SGL wonder rushing doesn't bother me that much.
Is it a lottery? Yep, but does it impact the game? Only if you're an intense micro-manager who can't stand the fact that something didn't go your way, IMHO. I agree that GalCiv had much WORSE random events, and other games, such as Morrowind, as relatively easy once you get to level 20 or so, the risk is pretty much gone if you've done just a few minor things correctly.
I have yet to see a SGL for myself in any of the games I have played, and I have discovered probably 200+ tech's first. If the AI get's a SGL and rushes a wonder I adjust and move on. No Hoover? Build solar or nuclear power plants when they are available. No Sufferage? Build lots of police stations and raise luxury taxes and end war's as quickly as possible.
The game can be won without ANY great wonders having been built or aquired by the player so I don't see what the game-breaker deal is. I am not saying it is not an issue for some, obviously, just that IMHO, the wonders in general are ALREADY "uber presents" so to complain that now you can get them easier than at other times is missing the fact that they can essentially break the game or make it much, much easier to begin with. If you don't believe they unbalance the game completely anyway, look around and see how many people recovered from a hole they were in by building ToE first when they were 5+ tech's behind and were able to trade their way to parity. How many times have people built or aquired the GL and then turned OFF research and saved cash that later put them ahead of the pack with no real chance of losing.
We should remove all wonders from a game and then play on Emperor or above and see how the game plays out for once, mighbe interesting to see how well things go without these huge crutches being around to begin with.