No. All you really need is to make sure that you don't open attachments from people you don't know, and don't run peer2peer software, or download any torrents, and make sure you have WPA2 encryption if using wireless with a non-dictonary password, and make sure the computer isn't in plain sight for any thieves and you should be OK.
Is SecureMac a program that is worthwhile and, in fact, good for your iMac?
There is no such program. SecureMac has two products and a few specialized freeware Trojan removers. The commercial products are MacScan and SecureScan.
For a critical review of the former, an anti-spyware / anti-malware app see MacScan disappoints.
I've just started to look at SecureScan. It's more of a cleaner app to ensure privacy on a Mac. I don't personally see any use for it, yet.