Just to add my own two sporebucks on this issue...
Firstly, Patch 3 wouldn't work for me; I had to uninstall-reinstall to get that to work, which blessedly it did. Then I splurged and got C&C, and went to install it, and I got the infamous 'Spore is not installed' error. After some poking around on the official forums, there was a theory going around that it couldn't find Spore if you installed it under a different language setting on your computer.
I typically run my computer on Japanese mode so I can play.. ahem... imported games. Now Spore installed and ran just fine under that mode, it didn't care-- but apparently it normally installs with a little (TM) in the directory name structure if you use the proper western/unicode language setting. Mine didn't have that, and I didn't know what needed to be altered where... so I uninstalled/reinstalled AGAIN, as C&C refused to see Spore without the proper little (TM) symbol in the directory name. Not even an option to MANUALLY locate Spore-- if it wasn't where it was supposed to be, it just said I didn't have it.
And this time, during the uninstall/reinstall, my saves got corrupted somehow. >_< I have all of my critters, still, but all of my planets are gone. My whole galaxy is tablula rasa. The parts are okay, but not really worth all of the pain it took through to install the damn thing. I really, really, REALLY they fix this problem in future parts packs. >_< Really.