Are there any concepts or formulas that are used in specialist/other that can be applied to methods to solve more difficult problems easier? If so, are they worth learning at this point?

The absolute value function is quite handy: \[|x|=\begin{cases}x,&x\geq 0\\-x,&x<0\end{cases}\] especially in integrating functions of the form \((ax+b)^{-1}\). Instead of case-breaking, one can simply write \[\int\frac{1}{ax+b}\,\text{d}x=\frac{1}{a}\log_e|ax+b|+c,\quad a\neq 0,\ \ c\in\mathbb{R}.\]

Some knowledge of vectors is sometimes useful when looking at geometry in the plane. For example, to find the angle between two lines, one can form two vectors \(\mathbf{a}\) and \(\mathbf{b}\) that are parallel to those lines and then use the fact that \[\mathbf{a}\cdot\mathbf{b}=|\mathbf{a}||\mathbf{b}|\cos(\theta).\]

I seriously doubt it, but partial fraction decomposition and a few 'advanced' integration techniques could be useful in verifying your answers.

I do want to echo DrDusk's point though. The questions

**will not** require any knowledge in higher level courses. If you're finding that you want to apply a concept that isn't thought in Methods, it's more than likely you are overthinking the question. Of course, there are exceptions to this though.