Andrew
You'll find a 10 or 12mm ( about 2mm exit pupil) about ideal for fainter galaxies. The arms will stand out much better with the higher power.
There are brighter galaxies around which you should turn to like M83 and NGC 253.
It is certainly hard when you are starting out to re adjust your expectations when you are use to looking at photograghs. All I can suggest is to practise marveling at what you _can_ see, rather than what you can't .
I firmly believe that a long and happy life as an astronomer comes from the ability to see things in the 'mind's eye' with a little prompting from the telescope. A large aperture isn't really that important; a dark sky and an imagination to see what is really there is much more so
