When I first started my blog I didn't want any comments because I didn't want any SPAM. Then I tried needing registration to comment. I didn't get any SPAM, but I didn't get many comments either. Then after installing a few plugins I allowed them - but only visible after I moderate them.
This is what I still do. It does take a bit of time to do the checking and weeding out. But most of the comments I approve are OK and many are even helpful for the feedback they give me about my plugins.
True, the SPAM to legitimate ratio is like 9:1, but I have no problem keeping up with it at the present time. And for my blog the good comments are worth the trouble of dealing with the SPAM.