Step 1: Identify the intercepting line.
The line $x+1=0$ simplifies to $x=-1$, a vertical line parallel to the $y$-axis.
Step 2: Intersect $x=-1$ with $3x+2y=5$.
$-3+2y=5 \implies y=4$. First intersection: $(-1,\,4)$.
Step 3: Intersect $x=-1$ with $3x+2y=3$.
$-3+2y=3 \implies y=3$. Second intersection: $(-1,\,3)$.
Step 4: Compute the intercept length.
\[\text{Length}=|4-3|=1.\]
Step 5: Interpret the result.
The vertical line $x=-1$ cuts a segment of length 1 between the two parallel lines.
Step 6: State the answer.
\[ \boxed{1} \]