It depends on what "help" constitutes to. I think they should not help poorer nations directly. This is because poorer nations are often poor because they have corrupt Presidents who will eat all the aid they get from foreign nations.

However, real help can come through foreign investment especially in mining/drilling and agricultural sector.

As said above to invest in different sectors. Considering mining and importing of raw products by richer countries. They can help out the most by making the technological advancement in the country from where they import products. Products like timber, silicon, and other materials widely found in developing countries or MEDCs and LEDCs. They can process these in the home country and import the final product with a value added. This act can actually harms HEDCs, their exports will be down. GDP may decline and more amount of money spent on importing goods.

Economist state that US is the strongest economy, China by 2015-2020, India by further half a decade/decade or so. This can be proven wrong as their only aspect is GDP. US's 95% of GDP is in debt, 14.3 trillion US Dollars are in debt with US owing china a massive amount. China is a developing country and still it has helped US. This may not be the case with bangladesh and other LEDCs, their NGOs are working very hard and all are on their track. Particularly, richer countries should help only when LEDCs are in need of that.

helping poorer nations should take the form frankly of showing them how to make themselves attractive to investors. anything else creates pain.

This is not always feasible. Farming, fishing or whichever you chose will not always be managed as sustainable resource. When people overfish, overfarm or do something out of the capacity of nature it always harms economy in long term benefits. Take an example of forests, they are also primary sector's investing area as logging. Selective logging if not practiced can lead to total deforestation and close doors for all investors in that country. Natural resources are finite. Laws and enforcements need to be created.
Mining is also primary sector, it will clear all the vegetation, if practiced overcast, if shaft-underground tunnels. They all will be destructive, mining has positive impact only on economy if world prices are higher, some mines may be shut down due to low prices. These creates fluctuations in employment also. Mining also needs training employees, unlike the above post said.

If richer countries invest in secondary sector there will not be any pressure from environmental organisations. It needs training but guarantees long term employment untill the sector is open. They close when raw materials decline as happened to automotive industries due to tsunami in Japan. Raw materials are cheaper than processed products, if secondary sector is focused it will be all hope and boon to the government to rise above their poverty or status of LEDCs. Tertiary sector is also vulnerable and depends on others as do other sectors. Processed products exported fetch more profit than raw materials which are obtained by vast destruction of nature.

Not on the fence- no 50-50.

Dubai was built on desert.
South Africa was an apartheid state.
And India has been screaming hunger for decades.

But showing them how to attract investors can hamper the progress of the 'teaching' countries. So, why would they do it anyway?

Lol Astar. 

Investors make money, true. But resources are scarce. Investment should be designed wisely, at the proper time, in the proper sector, for the proper future. Not in any dig-anywhere hole.