Reading over my last post, it sounds a bit like I'm heading into some kind of Knitting Dark Place - sorry about that (though thanks for the lovely comment, it did help me gain a little perspective). I read it a few times after posting and decided that what I needed was to assuage my guilt.
I could not find a pattern good enough for this yarn. There were several false starts. I tried socks with different patterns, but they looked way too chaotic no matter what. I was not happy, stamped, stomped, shouted at the yarn a bit (particularly 'too much entropy!' and 'stupid unicorn barf!'). I then shoved it to the bottom of my knitting in tray and tried to forget about it.
Then I started to get guilty about everything under the sun, including that I'd not managed to find a project to do justice to this beautiful yarn. At some point, I was moaning about this to my lovely housemate, who is both a knitter and one of life's 'doers'. So she did the leg work, found me a fabulous pattern* and I just had to cast on.
*actually, she found me half a dozen patterns, but we decided that this one was the best.
Pattern: Le Weekend [rav link]
Yarn: Toddy in colourway Spectrum, by The Yarn Yard.
Needles: KnitPro interchangeables in 4.5mm (5.5mm for cast on and cast off).
I knitted all the way up to Aberdeen and all the way back, and basically finished the whole thing then - but then I spent a week thinking about how I could possibly use up the rest of the yarn and then deciding, with the beautiful shape and all the short-row shaping I'd just done, that it would be best just as it is. SuperHousemate has solved this one too, and suggested I knit a few sets of baby booties out of what's left - after all, they don't care how crazy the colours are!