If you decided that moderating comments is the best way to deal with spam, there's a new option to enable comment moderation only for old posts. I'm not sure if Blogger's default value of 14 days is the best option, but you can change it to any other number. This way your readers will be able to comment on the recent posts without moderation, while the visitors who find older posts using search engines or links from other sites will need to wait until you approve their comments.
Blogger > Settings > Comments
Moderating comments (Blogger can't detect identical comments)
I still think that Blogger needs better tools to filter comment spam and I'm surprised to see that Google can't come up with a real solution like Akismet. The spam filter could also be used in Google Groups, orkut and other community sites.