Immunity/protection overlap?

I'm beginner/intermediate, and have been periodically changing/refining what I have running. Currently the active lineup is Comodo Firewall 2.4, Avast Home, and Threatfire Free. (They all get on well.)
Plenty of demand scanners available. Run a full scan periodically, alternating the scanners, nothing is ever found of any significance. (As should be the case.)


The main question:

SpywareBlaster 4.0 is installed and updated regularly. Ditto the MVPS Hosts file. Additional (or seriously overlapping) immunization is available via Spybot.
But is it wise to have more than one immunity application applied?
Perhaps the Hosts file by itself is enough; does SpywareBlaster add a worthwhile layer. Would activating the "immunize" function in Spybot add a significant worthwhile extra layer? Often more=less, or at least, no extra benefit. Prefer to cut back to just one of these, whichever will provide the most worthwhile protection.
Using Firefox with adblock plus and noscript. It is noticeably slower to open than IE, but seems to be about the same speed for loading webpages.

XP SP2, 2G RAM, AMD 3500+ (Single), everything patched/up to date.

Thanks for any advice/comment.

 

If you want immunization, better just use one: SpywareBlaster (and not Spybot S&D)

That said I dont care much for immunization. HOSTS file is a maybe for me.

 

I use MVPS & HpHosts files with HostsXpert 4.2 to merge/manage the files. Also use WOT toolbar. This provides a lot of extra protection.