The suggested tags are often useless so I wouldn't go to all your hubs and add them, but editing your tags can be a great way to boost traffic.
I use google's keyword tool and google wonderwheel to find highly related phrases and also the keyword section in the hub stats often gives me ideas for new tags.
Add some broad tags and lot of specific ones (and make sure you add your main keyphrases). Broad tags I'd add on a hub about how to get pregnant for example, would include health, women's health, fertility, pregnancy. I'd also make sure I added how to get pregnant, get pregnant, pregnant etc.