We bought in 2007 fully understanding and anticipating a crash.
What it boils down to is how much you need to move and whether the move is longer term.
If you are buying with the view that it's about your need being great enough and you are in it for the long haul the decision shouldn't be about how many much you might lose or how you might be in negative equity. The point is you are there long enough for it not to be an issue.
If you are renting now you have to consider how much you would spend on rent - so for first time buyers, getting a house usually is the right step provided you think you will be there for at least 5 years or you think you can over pay your way out of the negative equity. You have to factor in how muhh equity you build up and how that will affect the interest rates you may pay further down the line too. You want to be finishing your mortgage when you are younger, so delaying buying will usually affect that.
If you are up sizing it comes down to whether where you are is sustainable for the foreseeable.
Don't stay put waiting for a crash on the belief you will be able to get more for your money. It's unlikely to make any difference. You will find it harder to get a buyer yourself and the rules on lending with get tighter/more expensive which will restrict what you can get.
In our case if we had not have gone for an opportunity we saw, we probably would have been priced out of the area for a good 5 to 7 years when the market bottomed out. We would have had to rent or buy elsewhere which probably would have meant a very different life to the one we have now.
My point is plan for the life you want based on the opportunities you actually have rather than the chance of the opportunity you may get but equally may not get which involves you having to compromise now.
In the long term house prices (and the overall cost of housing to you including rent, changes in interest rates) will tend to sway to being cheaper / better for you if you start now.
Where you have issues is if you plan to buy for shorter periods and move on or if you are likely to have a significant change in circumstances. So if you are buying a two bed and plan to start a family (or accidentally start one) in the near future or you are liable to need to relocate you will run into problems.
How stable is your lifestyle is the big question. If you work in leisure or another vulnerable luxury industry I'd be more cautious unless I was very confident that should the worst happen, I'd get another job quickly. How future proofed in terms of lifestyle rather than finances is the big question.
For us, it made sense to buy at the top of the market. And still did in retrospect. We'd probably be a lot worse off now if we hadn't.
Others may well say differently, but I don't think the price on the house alone should be the only consideration.