To be quite honest, there were no positive effects of China being conquered by foreign interests. True, the open door policy meant that China would trade with the world, but the Chinese didn't want to do that... ANYTHING that China was MADE TO DO DUE TO Imperialism only benefited those who conquered them.
The imperialism had one positive effect on China, that was to make people of China realise the emperor and bureaucrats didn't have the ability to safeguard the land and protect their safety.
The incompetence of governance brought China defeats in battles with the imperialists and unequal treaties to its people. The door of Chinese long lasting close economy was opened by cannons. Opium flowed in and treasure flowed out, increased the burden of the nation. The imperialists scrambled for spheres of influence with each other, torn apart the once completed territory, the country was at a crisis.
Under such circumstance, people couldn't undergo suffering the oppression from both inside and outside. They rose up for their own survival, powerless but numerous. They want their fate in their own hands. At that moment, the struggling against imperialism and feudalism was begun.
There was a famous map in the link below that depicts the spheres of influence and China's political situation during the imperialists invasion. It was in cartoon form and used animal images to represent fierce intruders controlling vast areas of China whilst corrupt Chinese bureaucrats still daydreaming inland. The comments around the map means 'the situation is clear at a glance, no more words are needed'.