Not quite paddy, I would consider upgrading if the market is right. Suppose I choose to upgrade to something 50% bigger and more expensive. Thats a 525K house, I need to spend 525-350=175K. If the market falls by 50% then this house becomes 262.5K and my house is 175K. That means to upgrade costs 87.5K instead of 175K. I also save on stamp duty and solicitors as they are all based on %.
that does make a crash sound attractive alright
although I'm not sure i'd be relying on things turning out that way!
and a 50% drop would have a massive effect on the economy too; so perhaps you won't have a job?
(unless you work in our civil service, naturally)