Help me justify £1600+ for a f2.8 70-200mm VRll ;)

OK... so I have a standard 18-105 kit lens for my D90 and a 60mm macro lens....

I am sure I NEED a longer focal length, faster, better in low-light lens to get some really good shots..... don't I??.....!

See, bit of a quandry at the mo - I have had a bit of commission paid to me at work so have the money. However, I also need to be fairly sensible as have a second child on the way in November, so won't be working (at least for a bit, or unless I can get my photography good enough!) and also want a Mac (which by the time I've configured it with the solid state memory, 27" screen etc etc comes to mucho dinero in itself

Hubby has been my voice of reason saying maybe we could afford Either lens OR Mac but probably not really both..... Oooooh, the decisions! Help me!!!