Small Business Investment Promotion Act - Amends the Internal Revenue Code, with respect to the expensing allowance for depreciable business property, to make permanent: (1) the increased $200,000 expensing allowance for such property, (2) the increased $800,000 threshold amount for such property over which the expensing allowance is reduced, (3) expensing of computer software, and (4) rules for the expensing of qualified real property. Eliminates the termination date for exercising an election to expense property. Allows an inflation adjustment to the dollar amounts of the expensing allowance for taxable years beginning after 2014.