It can be argued that patents are more effective for older fields than new ones. In 1992 people where building high quality cars engines that are much like today's engines and all patents protecting a 1992 engine has expired. So, any new patent must be a non obvious improvement on a fairly high quality design. Software and DNA patents can still cover obvious things because the field has moved so rapidly.

However, it seems like most fields are integrating improvements from computing so there is a lot of low hanging fruit out there.