Hi froggie,
If it is performance improvement I really want, I would start it fresh (new installed operating system). But of course I have to consider the hardware like the RAM and the speed of the hard drive as well (assuming I cannot do anything with the CPU).
As for RegCure, I cannot say as I do not use it nor know anyone who does. On the other hand I suggest you try the steps here:
Is your PC running slow...?