Is it worth buying a few extra terabytes to backup? I simply don't have enough free space to even begin backing anything up.
0: http://www.newegg.com/Product/Product.aspx?Item=N82E16822178...
They offer a 30-day trial. If you try it, like it enough and are willing to wait, they often have promotions for the first year (for Black Friday last year, it was a tiered discount depending on how early you signed up).
I crash my 100k dollar car, and I think, damn, I'd give 100k to get it back. But when insuring it, I don't pay 100k for insurance! You have to take value x probability of loss to arrive at your X.
Just multiplying by the probability is what's known as "risk neutral" - it works and is a very good approximation when the dollar amounts amounts are small compared to your net worth. It tends not to be a good approximation when the dollar amounts are higher.
Of course, a realistic analysis would also account for the fact the the "data loss insurance" itself is probabilistic, but this is a start.
You really need to sort out something for passwords; software registrations; and logins. This is a tiny bit of backup, but it'll make life easier if your drive dies.