What is the ideal length? Should you try to use most of those 1,000 characters? You'll get different advice from different college counselors and admissions officers. A tight and engaging 85-word Short Answer is certainly better than a repetitive and rambling 170-word response.
That said, 150 words is still very little space in which to elaborate on a work experience or extracurricular activity. It takes less than a minute to read 150 words. If a college has true holistic admissions (a requirement for the Common Application), they want to get to know you as a person, not as a bunch of grades and numbers. Your writing is one of the few places where this can happen. So my general advice (assuming your writing is concise, precise, engaging, and insightful) is to take advantage of those 1,000 characters you've been given. Read more in this article on the ideal length of the Short Answer.