Would it be enough to increase the frequency of the blinking of the caret. Seems to me that a frenetically blinking cursor would be more easily seen.
Though TextMate doesn't respect the following system settings, maybe it should?
defaults write -g NSTextInsertionPointBlinkPeriodOff -float 0.1
defaults write -g NSTextInsertionPointBlinkPeriodOn -float 0.1
This comes from the following SuperUser post, which is actually about disabling the blinking, but seemed relevant any way.
Also some of this issue could be helped by, yet another, request for the "highlight current line" feature.
Thanks,