There are always dangers with modifying the registry which could indeed screw things up for installed programs.
The age of your PC has little to do with the state of the registry. Even installing and uninstalling programs can add or leave behind things that aren't required.
I can't speak for the winzip registry optimizer but I've used CCleaner in the past with success. I'd always be wary of running any application that came tagged along with something else. There is every chance that the additional application claims to be something it's not.