1. If I am not wrong, Bakhtiar Khilji was responsible for Nalanda's destruction. Ghauri probably did not wish to conquer all of India - it would have been unmanageable for him. I do think that his slaves, starting from Aibak onwards made a conscious decision to conquer and rule as much of India as they could. They had nothing to lose and really no where to go back to. Moreover, with their education, training, skills, and organization, they felt confident that they could conquer and rule India. After all, Sultan Ghauri did spend a lot of money on their education and training - treating them like his children that he did not have.
2. Historians have wondered about the difference in trajectory, had Muslim conquerors been Arabs of seventh century rather than Turks of the Eleventh & Twelfth. The two were different in their outlook and methods.
3. Aurangzeb excused his killing of Dara Shikoh. He would have done so with or without any reason in any case. Turkish princes routinely killed their brothers for throne. I can not understand or excuse such behavior, but that is how it was. Had Dara Shikoh won, he would have done the same thing to Aurangzeb. The same thing happened among Ottomans. Such practice ensured that the sharpest and most able of princes occupied the throne. As much history as I have read, I am sure that Aurangzeb was the ablest among his brothers.
4. India was a prize. But it took superior organization to take it. For people who feel hurt that Muslims conquered India, I can only say that conquest is not a random happening. It is result of superior social and organizational set up. Indian society was divided and though it put up a lot of resistance to conquest, the divisions eventually mattered negatively. The same thing could be seen with Indian response to the British who came in with superior organization and conquered India mostly because of its divisions.
So my friends. Anything that divides Indians is a bad thing. Divisions always did them in. Believe me, if Indians do a really bad job in this department, others will step in once again.