You don't need an MBA to be a successful entrepreneur (see: Bill Gates, Mark Zuckerberg, and I'm sure a ton of others who are less famous). What the MBA will provide you with is a thorough grounding in all aspects of business beyond your existing marketing skills (finance, operations, accounting), which you will need to put together a compelling business plan to secure financing for your business, not to mention to run your business. Also, it will allow you to tap into a network of other successful entrepreneurs and supporters of entrepreneurs (such as VCs) that will help support you as you launch your business.