Some have better equivalents in GEGL (due to the preview on canvas) - maybe someone will find it useful with a bigger preview - then replace the gradient-flare.exe file with the downloaded file (...\lib\gimp\2.0\plug-ins\gradient-flare\).
Remember to archive the original plugin.
In the original file gradient-flare.c only the following changes were made:
from (line 75,76,82,83):
#define DLG_PREVIEW_WIDTH 256
#define DLG_PREVIEW_HEIGHT 256
#define DLG_PREVIEW_MASK GDK_EXPOSURE_MASK | \
GDK_BUTTON_PRESS_MASK
#define DLG_LISTBOX_WIDTH 80
#define DLG_LISTBOX_HEIGHT 40
#define ED_PREVIEW_WIDTH 256
#define ED_PREVIEW_HEIGHT 256
to:
#define DLG_PREVIEW_WIDTH 512
#define DLG_PREVIEW_HEIGHT 512
#define DLG_PREVIEW_MASK GDK_EXPOSURE_MASK | \
GDK_BUTTON_PRESS_MASK
#define DLG_LISTBOX_WIDTH 80
#define DLG_LISTBOX_HEIGHT 40
#define ED_PREVIEW_WIDTH 512
#define ED_PREVIEW_HEIGHT 512