Switch to ClamAV and then send an actual written letter to Trend telling them you switched. (
link)
If you practice safe sex... err... surfing you have little to worry about in terms of viruses. I use AVG and I am behind a Linksys residential gateway. This is fine for anyone who has more than half a clue.
Buying software is for consumers. There are plenty of good free alternatives. ClamAV or AVG will do the job.
Software firewalls are basically crap. They are known to have significant flaws and are a real PITA.
There is nothing wrong with testing on bi-weekly basis. You will want to test if you find yourself in a "WTF did I just click on" moment. Also, you need to make sure you do the tests. It would be a shame to find a real problem and realise you have been "meaning to get to that" for six months.