I'm trying to weigh up the differences between these two - is the autiobiography really worth the extra £10K?

Look at the standard fit items available on each. Does one give you more than the other? If the AB gives you stuff you will use and enjoy then it's worth it, if it doesn't then it isn't.

If you mean "will the AB be worth more to a similar degree when sold in X years?" then no one can tell you. It's all guesswork.

Spec'ing a car based on what someone else might want in 3 years is a mug's game. Buy what works for you at the time.  2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed