Too Long; Didn't Read
Game jams are fun and can be a great learning experience but they can also be stressful and tiring. The game you make will likely not be marketable but it’s not about the product, it's about the process. There are successful indie games like Titans Souls that were prototyped in a game jam so it is possible to end up with an idea that is a sellable game after some post-jam polish. Make a short game and show everything good it has to offer right off the bat.