I had great gfx problems with Mario Tennis and default 1964 plugins, now I can play it without problems (only flickeing graphics in replay videos) with this configuration:
Video Plugin: Jabo's Direct3D8 1.6
Sound Plugin: Jabo's DirectSound 1.6
RSP Plugin: Jabo's one taken from Project64
then you need in Plugins->Video Settings menu to uncheck `Hide Advanced Settings`, and go to menu label Advanced and check `Force alpha blending`.
Hope this can solve for you, too, this is a funny game to play with other friends thanks to 2p/3p/4p capabilities.