If you reinstall the OS you will have to install all the applications once again. There is no escape from it. Slowing of an OS has many culprits viz. registry, unnecessary files in Windows folder that are left after uninstalling any software, unnecessary services added to startup etc.
A clean install will definitely give your system a boost in performance and speed.
To answer your dilemma, you can do this one time activity. Have a clan install of OS on your clean hard disk partition, install all the needed softwares and then make a ghost image of that. This image could be used next time you need to reconfigure your PC afresh.