Many artists work in several different mediums. I, for instance, work in encaustics, acrylics, pen and ink and so on. I find that it broadens my understanding of specific techniques and allows me to explore my creative talents in new ways. I would recommend expanding your artistic repertoire to anyone - without question. However, selecting a broad range of work that spans several mediums for submission purposes can (will) hurt your chances of being selected for a show/publication.
I understand that it is important for artists to show their versatility. Perhaps you're hoping that if the juror isn't fond of your oil paintings they will still find your watercolor or photography of particular interest. So you submit a few of each in hopes that one of your artistic endeavors catches their eye. There in lies your biggest mistake.
A juror is looking for a cohesive idea and style behind your submission. They are not interested in a overall review of your artistic talents. They want to feel a connection among the pieces you submitted. They want your work to speak to them as a unique collection - not as a jumbled collage.
As you grow as an artist and continue to develop your skills in new mediums, be cognisant that techniques acquired while exploring one medium can be applied to all others. Light, dark, shadows, composition, color - all of these elements are important across the board. Use all of your artistic explorations to develop a focussed series of work in one medium. That doesn't mean you have to stop exploring the other mediums you are interested in. It does mean that you should choose one particular medium (for the time being) to concentrate on, develop, and explore. When or if that gets boring, begin again with different ideas/mediums. Utilize and focus your skills to help you create a cohesive collection of work.