Thanks for the replies lads. Turning into quite a popular thread, who'd have thunk it.
Bit the bullet and deleted some games I haven't touched for ages. It really pained me to do it though! I too am from the age of dial up and am very used to hoarding/ backing up data.
I am from that age also, but you must be new to a fast line, after a while you realise you can download anything you want fast enough. Any game you want at most is a couple of hours download away. Just think of it as, why should you spend money and store stuff when you can let them store it for you, just download the specific content you need when you do.
Also do not forget, steam shows the space needed on hard drive most of the time, keep an eye out for the download size. A game I downloaded last said 15gb, but was 8gb to download for example.