The shifts in ideas about the value of Indian culture and politics are quite complex. Robert Travers has an excellent book on English ideas of the Indian constitution. He tracks how the British shifted between respect for the Mughal tradition through to latching on to the idea of a primitive Hindu constitutionalism through to the more general denigration of Indian political history.

I'd argue that the key group for marking the change you're interested in was the utilitarians. Jennifer Pitts argues that Bentham had a generally dim view of empire and civilizing missions, but the Mills, particularly James Mill though John Stuart followed him, were very much keen on making the Indians fit to govern themselves (by which I mean, subjecting them to "legitimate" tyranny until such time as they were liberal utilitarians). There were also a host of influential utilitarians in India (see Stokes's classic on the subject). Macaulay was certainly not a utilitarian (or, at least, he famously disagreed with Mill), but his approach to Indian affairs, especially in his famous "Minute" on Indian education very much reflects that radical-cum-liberal approach to empire. Sort of a secular offshoot of the mission zeal of the Church. You could call it liberal imperialism. (Though it's wise to mark within that the difference between the free trade liberalism of the Manchester School, which was critical of empire but not opposed to empire as such, and the liberal civilizing mission of people like Mill, Harriet Martineau, etc.)

Good reading on the subject: Pitts, A Turn to Empire

Schultz and Varouxakis, Utilitarianism and Empire

Travers, Ideology and Empire

Stokes, The English Utilitarians and India

Claeys, Imperial Sceptics

Edit: also, Mehta, Liberalism and Empire