"Worthwhile", I don't know. I guess it depends on what your product is supposed to do.

My product is http://smallpayroll.ca, it's a do it yourself payroll site made for people who don't know anything about payroll. I freely admit it looks like crap. But of the handful of people that have tried it out and paid for it, I haven't heard "this looks like crap". What I hear is "this product makes my life so much easier"

Could I get more conversions with a better design? Maybe... But I know for my product it's not preventing me from getting paying customers.

(As an aside, I've often thought there should be a place for people like us to find designers that know how to work with applications instead of just designing web pages.)