You and I share the same paranoid computer world view. If you start with a clean version of Windows 7 and spend a day or two fooling around with it, and then install the multitude of updates available it is amazing how much things get bogged down. I am always a little disappointed by the performance hit when running virtual Operating Systems. I guess that is one argument for a newer computer.
I would think getting a anti spyware program like Malwarebytes and a anti virus program like Webroot then you do not need to update Windows.
One man's paranoia is another man's practical world view based on decades of experience in the Computer/Technology field. :-)