Finally, borrowing can save you tremendous effort in design and implementation and often in maintenance as well. At some point in most projects you'll probably feel that you've done all the copying that you can, and that you've got design problems that really call for new solutions. Make another try at locating a system that does the kind of thing you need. Ask more people for leads and ideas. Make sure the new feature is really important.
Innovation is risky and expensive.
It's just not worth it for a small refinement of your design. The new feature has to be central.