Thanks for your response,
I've been manually approving for over 10 years now myself and have noticed many signups don't verify the email. I've wondered if the verification emails end up in spam folders, or they just don't get it.
I agree, generally it has been easy to spot the spammer registrations by the info they put in and a quick Google search.
I'm going to run for awhile with the settings above and see how it goes.