Of the items listed the only ones that need manual updating are Spybot and Spyware Blaster, and those two are probably not essential given the nature of the other plugins. They're effectively block lists, and given the behavioural scan techniques of the other products they are probably superfluous.
However the other products are needed.
"Common sense. Decent anti-virus" Doesn't wash nowadays, especially in the day of the supercoockie.
A large number of "safe" web pages are compromised nowadays, and a lot of A/V programs don't block web attacks. They should, but they don't.
As for slowing the system down - it does, but insignificantly.
The final point is that most current computer users either don't have the knowledge, or else are too thick, to browse safely. You HAVE to load the machine up to protect users from their own idiocy.