Personally, I think it's pretty easy to get around if you stay onsite -- you can easily take a bus to the Expo from your resort, and also take the busses right to the start line (or the monorail, if you are staying at a monorail hotel). But I am one who really likes to stay onsite in any case, so I'm biased.
For marathon weekend, all of the hotels are designated as host hotels (well, I'm not sure about SOG, but all the others are). You will find participants at all of them. I think the greatest concentration will be at the Values, because many people come just to do the race and want to stay as inexpensively as possible. I noticed that the lines on race morning are the longest at the Values, but that could just be my perception. We've stayed at POR, CSR and WL, and found them all to be fine for the races. I stayed at AS Sports for the Princess, and that line was pretty scary, but it worked for me.
The only downside I can see is that depending on when you finish, you can have a long line waiting for your bus to get back to your resort, and the line is longer if there are a lot of people at your resort...but that said, they run the busses continuously and I don't know if it would be any quicker to try to drive off of property. Oh! And if you are onsite you have to catch your bus pretty early, I'm not sure if you could leave later driving since they close off the roads and it seems complicated to me to get around, but someone who has stayed offsite for a race could give better advice.
Enjoy your training and the race, Disney races are special!
Maria
