Last year I took about £150 and came home with a bit of change, maybe £20. But that included any food, a few beers and (possibly) train fare. However, I didn't really make any expensive figure purchases. I think the highest single buy was the three RID trainbots for £25 (two with box).
This year I plan on taking as much as I can save before the show!! Hoping for at least double that, maybe a bit more. I'll not necessarily spend it all, just want to have it available in case I see something pricey that take my fancy!
As far as the Sunday is concerned, I think there will be as much happening as the Sat. Things are gonna be split up fairly evenly between the two days, so they say.
Last year I kept myself pretty much to myself bar a few chats with a couple of the dealers. There was enough to keep me there till the end of the day.
However I do regret not revealing myself

to people I know from the boards. (Partly due to me not being great at making conversation with people I don't really know and partly 'cus I was on a bit of a downer at the time!)
Plan to make up for that this year though!