there will not be a great difference unless fresh install after you caught with virus & spy ware like that and affect system performance slowly..
just keeping updated drivers & software's including OS & good anti-virus with firewall , tools like ccleaner for temp file cleaning & registry fix if good enough for better performance..
best some people keep formatting the system once in 3 or 6 months & they belive that works..
Over time your computer can load up with rogue start up programs, and erroneous running processes.
Regular virus/malware scans can help, as well as checking your start up programs, and running processes. Look up what they are on Google if necessary, and stop the non vital processes, making sure your not stopping program you need, or something windows needs.
I personally prefer to get my PC to where I like it, then create a complete drive image. That way I can do a quick re-install of windows, than clone over my setup, without spending a day reinstalling stuff.