Are there any nontrivial spaces $Y$ so that for all weak homotopy equivalences $A\to B$, the induced map $[B, Y]\to [A,Y]$ is bijective?
This would be a property of the homotopy type of $Y$, and if $Y$ is homotopy equivalent to a space with has some kind of local structure under which very close maps (probably of compact spaces like $S^k$) are necessarily homotopic, then it probably won't have this property.
My idea is to use the following construction: let $L L^+ = \{ 0\} \cup \{ {1\over n} \mid n \geq 1\}$ , and consider maps let $L = \{ 0\} \cup L^+$. Then this hypothetical local property of $Y$ would ensure that the restriction $L \times X \to Y$ L^+\times X$ would induce an injection on homotopy sets. But $L\times X$ is weakly equivalent to $\coprod_{0}^\infty X$, and in the latter space we can have maps which are $f$ on $X\times {1\over n}$ for $n > 0$ and $g$ on $X\times 0$, where $f\not \simeq g$. Taking $X = S^k$ seems promising, since it is compact.
