When AVG8 first came on the scene it caused problems with Blaster and Spybot. This is possibly the reason for your reluctance. I understand these issues have now been resolved although I don't use Blaster or Spybot myself.
Over cautious? Not necessarily, better to be safe than sorry, although one Antivirus and one Antimalware is considered sufficient by many.
My preferences are AVG 8.5, which comes with AntiSpyware built in, Malwarebytes for good measure.