Rob,
I fully agree that it is worthwhile keeping a 'low res' eye on eta Car as often as possible ... you may even be the lucky one to catch it when it finally blows
The simple grating spectrometer, such as the SA-100/200, is very well suited for confirming faint SN and novae activity and an excellent way to start spectroscopy ... if I had my way it would be a compulsory first step ... and should be part of every amateur's toolkit.
I just noticed that I previously referred to the main and primary eta Car component stars. What I obviously meant was main and secondary, or primary and secondary, components.
Cheers,
Bernard