I think it depends what type of user you are. If you are an experimenter and tweaker who likes trying out new apps, live wallpapers, games, custom skins, rooting your phone etc then you need the security. But if you are more set in your regular set of trusted apps and services without much experimentation, I'd say forget the anti-virus - its just bloatware. I've never felt the need for it, coz I don't play games, have never tried to root my phone and I played with live wallpapers for like a week and got over it. The only thing that gets downloaded on my phone are app updates, emails, evernote syncing and the odd picture from whatsapp.
PLUS also consider how long you intend to keep your phone for. If you wanna keep it for a very long time, you might wanna watch those charge cycles: so charging twice or three times daily isn't doing your battery any favours. Having said that, I reckon the tweaker/experimenter will probably upgrade their phone more often, so it all balances itself out really. The non tweaker will probably keep their phone a lot longer - I've kept mine a good two years and it still runs gingerbread but I don't find myself wanting for much most of the time. So for my money, battery life matters more.