Hi C.
1) You see deeper as you up the magnification, up to about 1.5-2mm exit pupil, beyond which more magnification will not let you see any more stars. (Exit pupil = aperture / magnification = eyepiece focal length / telescope f-number).
2) You can see some of the brighter galaxies, but they are rather unimpressive compared with what you see from a dark site. NGC 253 is one of the easiest right now. Brighter nebulae you can see easily with quite a bit of detail in the brightest ones. But go for a drive to darker skies whenever you can. The difference between the suburbs and somewhere 100+km from Melbourne is like going from a 4-5" scope to a 12". Or in your case like going from a 12" to a 30".
