If mining activities begin to ease, there will be increased competition and squeeze in other parts of the engineering world like civil construction. WTP is QLD based (I think) and the State Government there isn't opening up the purse strings any time soon.
Margins are actually still high by historical standands (for those companies that are consistently profitable).
One issue with WTP is that it is a small operator - so one project screw up can have major impact on the bottom line. The reverse is also true of course. But from a risk point of view, if you want exposure to the sector but minimise individual project risks, WTP may not be the perfect candidate.