Eta Carina is almost one of a kind (well it is amongst bright stars

). It is a multiple star irregular variable of PEC class (peculiar spectrum). It goes through a semi-regular cycle every 6 and a bit years or so where the spectrum changes. It's also survived a false supernova event in 1841 (?) and is expected to go supernova any time (i.e. from now till 1-200k years)

. It would be quite a coup to have data revealing changes immediately prior to a SN!
Betelgeuse is a red giant that has been reportedly doing funny things like maintaining brightness and spectral class (I presume, because I've found nothing about that changing) but physically shrinking in size...

... something's got to be going on there.
Regor is just a nice bright Wolf Rayet star with excellent emission lines (as Eta Carina has), so there's opportunity to measure and monitor the radial velocity of the gas being ejected, etc.
Of course, planetary-wise there's always atmospheric absorption of the planets and their satellites to do, and measurment of rates of rotation, etc.
Al.