The Los Angeles Times has recently run a series of articles about what the paper calls "The New Foreign Aid". There is much to be said for remittances. There is no interfering government bureaucracy, and they money goes directly to the intended recipients. This is not always the case with aid projects. What remittances are not good at is the funding of public goods and large infrastructure projects; there is a problem with coordination.
Most of this money goes directly for consumption, some of it is invested in business. Could some of it be harnessed for conservation in poor countries? It certainly wouldn't be easy. If you don't have enough to eat, you won't spend much time worrying about the environment. But if money is raised as an investment in business, it might work. An example could be ecotourism. Money could be raised from immigrants' investment clubs, and where they don't have one, they could be encouraged to start one.
Here is an obvious opportunity for innovative Non Governmental Organizations (NGOs). The added advantage of this type of funding is that any NGO that relied on remittances for funding would be forced to be responsive to the intended beneficiaries of their projects. That would be a great step forward. The success of most NGOs depends on their ability to raise funds from donors, only indirectly on meeting needs of beneficiaries.
The money is there. What is needed is a new way of thinking.
Update June 20
It doesn't make sense to lump a lot of countries into the "poor country" category. Mexico, for example, is a middle income country. See also this graph from Gapminder, and look at the different trajectories of Korea and DR Congo.