Time to Format and Re-Install OSX?

I've had my 2.8 Ghz Intel Core 2 Duo MBP since late 2008. The only upgrades I've done were to bring it up to Snow Leopard 10.6.8, max out the memory to 8GB DDR3 and upgrade GB and iMovie to the 2011 editions. I have had many programs installed and deleted over the years and my 320GG HD is down to 54GB free space after deleting as much unwanted crap as I could find. Everything has always been running great up until the last few months where things have begun to slow down. Programs run slower, video is choppy and internet seems slow.

So, I'm thinking it's time to clean house, get rid of all the clutter and re-install the OS while upgrading to Mountain Lion.

Question is, I don't want to completely format the whole HD and lose programs I have installed, unless it's what you recommend. I have my original install discs and the Snow Leopard disc. I can re-install programs if needed but will GB and iMovie remain the 2011 editions? Should I format the whole disc or was that something I used to have to do with Windows but don't need to do with OSX? Thanks

 

Thanks, I'll check it out!