Is it worth drafting a backup kicker and defense in fantasy football?

I get 9 bench players. I filled in my bench with spare wide receivers, running backs, a quarterback and a tight end. What I'm wondering is whether it's worth drafting a backup kicker and defense (I realize I'll need them for bye weeks) that will just sit on my bench for most of the season. Instead, I'm wondering if I should draft someone who could be useful down the road (like Sage Rosenfels in case Brett Favre is hurt, or Daunte Culpepper in the event Matthew Stafford goes out) and just dropping someone to pick up a backup for the week I need it. Thoughts?