Please consider modifying the Ethernet and Wifi libraries (and others as appropriate) to set the SPCR to the required value in every entry point into the library that uses SPI. The SPCR could have changed value between calls to the library (e.g. the user has another device on the SPI bus). The current situation requires the user to read the library code to determine the required SPI settings and write code to set the SPCR prior to each call into the library. Its seems natural that the library should manage its own SPI settings.
if you have sample code you can post it as an issue on