Old subpanel in detached garage

[crdeantonio]

We moved into this home recently and have a detached garage with subpanel being fed by a 30-amp breaker from the main panel via conduit buried underground. I'm redoing the garage with storage and a workbench area and wanted to run another circuit, so I had a look at the subpanel and it's causing me to pause and question whether or not it was ever installed correctly. The garage is very old, so it could be an install done prior to modern codes, etc., but I wanted to get the opinion of this group. Here are my observations:

• The subpanel is fed with 3-wire (1 hot, 1 neutral, 1 ground). Everything I've read says that it should be 4 (two hot).
• It looks like the neutral and grounds are using the same bus bar. I thought this was a no-no for subpanels?
• There are no grounding rods anywhere around the garage. Is this a safety issue?

I have attached a picture of the inside of the subpanel. I'm going to get a professional estimate for replacement, but interested in hearing opinions on this install and what should be remediated.
Thanks!