We're planning a loft conversion, kitchen-dining room extension, new windows, rewiring, insulation, new kitchen and bathrooms, garden re-design ... and will spread it all over 5 years for cost and sanity reasons. It's a 1950s house which has barely been touched since it was built, but in a perfect location for us. We could never have afforded it, had it been 'done' already.
I've been, I actually won tickets via Mumsnet when Kevin did a webchat and got to meet him on the day!
I think it'd be most useful if you go in there with a plan of what you're looking for and having done your homework beforehand on prices you can obtain elsewhere.
Armed with the fact that you need, say, a bathroom suite and you've found one you like and know it'll cost you £X to order online... You're then in a good position to examine what's out, speak to representatives of the companies and then haggle over prices.
Alternatively, Grand Designs Live might be a good starting point if you've no idea exactly what you're after and are just scouting for ideas at this stage.
There was a good range of exhibitors, from construction to interiors to decor to services. Lots of things out to see, try and explore, though the queues for some sections were quite long.
If we ever manage to sell our current property and buy the house we're after, that's going to be a long term project to get it just the way we want. In a few years time, I can see us going back to Grand Designs Live as part of that!