From a recent email I gather this is very off-topic, so I will try to be brief in my reply.
(Geneva.CH.EU.*) since 3+ years. I can say from my experiences I couldn't
make any kind of communication between botnets and spam. Most Trojan codes I
have looked into doesn't have any command/action to make users send spam
emails and such however they try infecting others by different ways that
port 25 can't avoid.
Many of the infected systems have more Trojan horses installed than the original infecting agent. Many Trojan horses have spam-sending or relaying capabilities.. or even just anonymity capabilities or ID theft/DDoS options. Thing is, there are always more options that can be later installed.
As to you not seeing them.. I suppose it's as simple as you not seeing enough of them.. count your blessings.