Your analysis on high correlation between export and private investment is correct for past private investment. And it is unlikely to see manufacturing-based private investment given high idle capacity and low utilization.
However, what Thailand government would like to see is when they invest in transportation/communication infrastructure, urbanization trend accelerates and private investment follows.
Yes, the government failed last year to execute big transportation infra projects.
But it has just launched bidding of four mass transit infra projects (Yellow and Pink as PPP, Orange on civil, and Blue Extension for operator) in the past two months for execution next year.
All will be translated into GDP number next year in a more meaningful way. So will private construction.
In addition, they accelerate the national e-payment policy execution urging banks to expand its electronic fund transfer & payment services at cheaper costs. Clearly this will see investment in network and equipment to better use the recently launched 4G network.
What you comment is the old economy that will take time to use up idle economy. But what they expect a crowding-in private investment is more new economy and urbanization acceleration.