The ability to draw is not something a person is born with; anyone can learn these skills. If you are going into any field of design you will likely be offered electives in Design Fundamentals and/or Life Drawing. Definitely take these classes as they will help you improve your skills at drawing and visualizing as well as to help build a credible portfolio enabling you to communicate with your peers and potential employers.
Design Fundies help build a foundation that all Graphics Arts are built upon and Life Drawing will help with taking your ideas and turning them into visual elements that help communicate your design solutions. Design ideas really don't mean anything until you can turn them into design solutions and that's only possible if your ideas can be explained whether in an animated powerpoint or a sketch on a napkin.
Truly the skill that is most needed here is Storytelling. If your crude scribbles and stick figures can tell a compelling story then drawing ability is of little importance. Just look at Don Hertzfeldt cartoons! A brilliant graphic artist and storyteller.
Still, being able to competently express your graphic and art abilities is going to be a huge factor in convincing potential clients that you have the skills and experience to achieve their goal. It is definitely worth learning drawing skills and can also be rewarding for other reasons like giving you new eyes upon the real world.
It all comes down to your clients' expectations. Are you offering them 3-4 mediocre mock-ups and expecting them to do your job of finding the correct solution by choosing the best one you have made available to them or are you an experienced designer that has confidently found the correct approach to the design problem and presented that as your assured and final design solution ready for application?