Rupert Costco’s analysis statement preceding what your first highlight in red states ( and the last and most oppressive of such measures, the Dawes Allotment Act.) The Dawes Act is what he was referring to.

From that article Costo said, "The IRA was the last great drive to assimilate the American Indian. It was also a program to colonize the tribes. “

But he fails to mention how it would assimilate. Since the enactment of the IRA, approximately five million acres of land have been acquired and placed into trust for Indian tribes and their members. That’s hardly what I call assimilation.

Your second highlight in red refers to voting. The article also states ( Those opposed to the Act feared that it would be detrimental to them because it would be controlled by the federal government. In the end 181 tribes voted in favor of the Act and 77 tribes rejected it.) All of the NY tribes rejected it and the only voting rules in the act were a no vote was to reject.

But confusion by the tribes does not change what the act did.

I agree with the Wikipedia synopsis. Congress did not pass everything Collier wanted and the BIA always did have oversight and traditional systems of government may have been better. But even that leads out with (The act has helped conserve the communal tribal land bases. )

But your question was at what point in time did the assimilation of Native Americans, their land and their culture cease to be racially and/or profit motivated?

The IRA was the point regarding individual Indians, the land and their culture being racially motivated. Legally that is what differentiated individuals from the tribal governments and from racial to political.

Collier made promises on his ideals and Congress did not pass everything he proposed. So if he said if you like your government you can keep it, consider the source from a true blue progressive. Yet, as you also noted 77 tribes rejected it.

As you also highlight in red ( The IRA did not let the tribes have their own governments that would be completely independent. Instead, it ensured that the tribes would remain under the supervision of the Bureau of Indian Affairs)

Well, there are three sovereign in the US Constitution and tribes are not one of them. So for tribes to exist they only do so under the auspices of the federal government as a trustee to a ward. So tribal governments will never be completely independent to the extent some fanaticize.

FIP changed in 1970 under Nixon with a Self Determination policy.

Congress passed the Indian Self-Determination and Education Assistance Act of 1975. It enabled the government to make direct contracts with the Indian tribes just as it does with the states, for implementation of programs and distribution of funds. Rather than the BIA administering programs directly, the government would contract with tribes to manage health care, for instance, or educational benefits.

In 1968, Congress had passed the Indian Civil Rights Act. The bill was to ensure provision of the Bill of Rights to the tribal peoples. But SCOTUS ruled that Self Determination left that up to the tribal governments, which are often the oppressor.

In the following years, Congress passed additional legislation to carry out Nixon's programs to develop a stronger trust relationship between the federal government and the tribes, and to allow the tribes to manage their own affairs.

Examples are the Indian Financing Act of 1974 and the Self-Determination and Education Act of 1975. The Indian Child Welfare Act "... recognized tribal courts as the primary and ultimate forum for welfare and custody cases concerning native children."By promising to look after the tribes' children, the ICWA contributed to the economic and cultural welfare of each tribe's future. The American Indian Religious Freedom Act "...recognized the integrity of native cultures." It ended the persecution of American Indians for such practices as the use of peyote in religion.

Since 1980, administrations have issued Presidential Memoranda on Indian affairs to indicate direction for increased tribal sovereignty. A 1994 Presidential Memorandum issued by Bill Clinton changed the way the U.S. Department of Housing and Urban Development supported housing programs. The Native American Housing Assistance and Self-Determination Act of 1996 consolidated grant programs for housing funding into a single block grant specifically available to recognized governments of American Indians and Alaska Natives.

http://historymatters.gmu.edu/d/33/
Alfred Dubray, a Brule Sioux born on the Rosebud Rex. In SD says It had a lot of advantages that many of the people didn’t see, such as making loan funds available, huge amounts of that. Farm programs were developed through this. Cattle-raising programs were initiated. Educational loans were beginning to be made available for Indian youngsters who had never had any opportunities before, hardly, to attend any higher institutions. Unless they just did it by sheer initiative, and if somebody is sponsoring it. So there was a new field there in education, and, of course, mainly the tribal governing body section of it—busy there, and they established their governing body and voted on their representatives and the council members.

I think it was difficult for the people to really recognize what they were doing for probably several years after that, until they got into the change.

Source: Oral history courtesy of Institute of American Indian Studies, South Dakota Oral History Center, University of South Dakota.

So some liked it and some did not. I don't like it either, but that was not the question.