Seriously, the best resource for improvement is your competition. Those who would luke in the shadows to undercut the price or improve on the quality or its value can help you improve your offering. So I say to you then..
“Steal from yourself, before someone else does.”
I know this sounds quite odd, but that is exactly what your competition does when you introduce a new offering. They analyse every aspect and attempt to either cut the production cost to bring it to market cheaper or they add more value to the product, making it seem to be better. It’s basic business. My suggestion for you is to create a team inside or even attempt to do this yourself if possible. It’s a great way to uncover design changes, cost cuts or overall improvements. Steal from yourself and act like your own competition to keep fresh, valuable and keep up the advantage.