What is the ruling on limiting one's contemplation (tadabbur) to the Qur'an without the Sunnah, or vice versa, and what is the ruling on belonging to intellectual movements that adopt this methodology?

If by "currents" is meant those who call themselves "People of the Quran" and reject the Sunnah, then these individuals also reject the Quran, because the Quran commands obedience to the Messenger (peace be upon him) and adherence to his Sunnah. It also explicitly states that the Messenger (peace be upon him) is an expounder of the Quran, and the Messenger (peace be upon him) foretold the appearance of this type of people.

Whoever denies the authority of the authentic Sunnah is like one who denies the authority of the Quran. It is not permissible to associate with them; rather, they must be called to the truth.

Contemplating the Quran is an ultimate goal for it. It calls to all good and protects from all evil. Contemplating and understanding the Sunnah is required for a correct and complete understanding of the Quran, for it is its expounder, and contemplating it is a sign of a servant's success [granted by God].

It is obligatory to contemplate both the Quran and the Sunnah, for together they constitute the religion of Allah.