I totally agree. Idle cash is evil and I'm assuming it would have to sit there for a bit while you decide on what invest it. Go with what you know and pay of your debt. Use the cash that you free up to start purchasing your income producing asset.Why not pay off the debt (assuming the student loan is higher interest than you will get in a high interest savings account, and the mortgage penalty is not significant), and then if you do find a good business, tap into a HELOC? While a HELOC might be a bit more interest than a mortgage, since you're using it for income purposes it should be tax deductible, which should put more money in your pocket, especially if rates go up.
Just brainstorming with you though, there's still too many unknowns to really say that's a good or bad idea, like how long you expect it to take you to find a new business.