it will make my blog look more alive and maybe more people (not spammers) will be interested in commenting when they see that others have commented?
Not really. If the comment actually has something to do with your post, and the same comment has not been left on oh say, a 100,000 other blogs, then people may want to get involved in the conversation.
Who want's to get into a conversation where a spam bot left "Great article! I found your information very interesting. Oh and BTW, please click on my SELL-JUNK-STUFF-HERE link."
Spam comments are like posts that have been lifted from someone else's blog. Unique (and pertinent) content will get you more visitors. Approving spam comments wont.
How do I know if a spammer's website is a malware/virus/phishing site?
You can't tell. But if it's spam then leave it in the trash bin. It won't help your blog's traffic and if you approve it then you are providing free advertising to someone else's web site.