Yeah, I'm thinking that might be my next big purchase too.
Though for me, it'd be more to replace my old, 'first generation' external hard drives, which take up a lot of physical space, don't have that much digital space on them, and are also starting to play up.
I've had them between 5-7 years though, so I can't complain too much.
I hadn't looked at hard drive prices since my masters year, so was surprised by how cheap 2TB is these days! It'd be nice to have everything on one drive (portable too!) as opposed to spread across four.
As for deleting series, I've had to do a lot of that this year. I've mostly focused on anime that have been licensed in the UK, the idea being that if I delete my fansubbed versions, I'll be more likely to buy them on DVD/BD.