I tested the Ozone free trial and it certainly does what I wanted - the spectral display in the EQ GUI is a superb feature I'd not seen before. Taking sambrox's 'best offer' advice, I actually managed to get the Mix and Master bundle (Ozone and Alloy) for under £190 from a US eBay seller, which I think is pretty good and was worth the bit extra in case I need any of Alloy's features for mixing.
Apart from a cursory look, I haven't tried Alloy yet (I'm out of the country on business until the end of the week). I'll have a proper play with them both at the weekend, but I think I will focus on learning how to use Ozone properly for now.
I'll also have a look at that free version of Nebula - sounds like some interesting technology.