Hi~
I just want to put in my 2c. Most of Downtown LA is a drag. Not very safe. Dont try to walk to Union station. Take a cab. Just say Union station. Dont act like you are from out of town. That way the taxi will take a strait shot, not the "scenic route".
But if you are coming back from DL at night, to DowntownLA please be careful! Me personally , I would stay at a hotel in Hollywood and take the metrolink or taxi to Downtown to your convention. You can catch the metro on Hollywood blvd. Hollywood is way safer than staying in Downtown (just stay west of Highland). There are some nice hotels down there like the Bonaventure,but it is surrounded by lots of dangerous stuff.
Everything in LA is actually pretty close but it is just blocked by lots of traffic. If you have any questions you can ask me. I would love to help.