I don't eat spam, but there isn't much you can do to it. I would be more concerned about the contents leaking all over my equipment. Spam is already cooked (and thoroughly preserved) so you just need to get it to the temperature you want to eat it at. I guess if I had left it out a couple days and it smelled ok, then I would boil it extra long just in case.
If you are concerned you could use pre-cooked bacon instead:
Bear in mind that once you open the package of Spam the pre-cooked element is no longer providing food safety. A better question would be: If I left an opened package of Spam at room temperature for a day, would bacteria grow on it. I'm guessing that the answer for that one is yes indeed.
In food science classes they have the 4 hours and 40 degrees rules. Never leave anything that can grow bacteria for more than 4 hours at a temperature above 40 degrees and below 140 degrees F.
Bad things happen.