Is it worth it to buy a 50mm 1.8 lens if my camera has a 1.6 crop factor?
No one besides you can answer this question.
A Cinema Prime Set pften constists out of a 18mm, 25mm, 35mm, 50mm, 85mm Primes (On Aps-C). It now depends on what you want to shoot. If you mainly shoot interior wides, the lens won't be of much use.

But a 50mm f1.8 is often a great - cheap option to get into blurrier shoots.