The queues don't really vary depending on the race, but rather on the characters. If it's Wreck-It Ralph, you could be done in a few seconds. If its Mickey and Minnie by the castle, it could be 5-10 minutes. Generally speaking, they move reasonably quickly. If there are 10 people in a queue (and thats about the average queue length), you're probably looking at 2-3 mins. I waited 5-6 minutes for Buzz Lightyear, but I wanted that photo so it was worth the wait.
There are definitely more photo opps on the longer races, but the queues dont get any shorter as the week goes on. The half marathon and marathon have the better characters, so realistically, you might spend more time queueing on those days. You really have to assess each opp as you approach them, and decide whether you think its worth the wait.
There were actually race marshals at the ride letting people know it was open. That's the first we knew about it. Might be worth asking at the expo to see if any others are open too.
We didn't do the race retreat so I can really comment on value for money. Our thinking was to get there pretty close to race start times (it's early enough without having to get there earlier for brekkie), and head back reasonably quickly after finishing for a nap before heading out for the day. Disney resorts offer marathon dinners and breakfasts for runners. We had a few of those. They also do a fuel box after the races which is very good. Everybody gets one. Not huge, but got some decent bits and pieces in there. Plus, there's more water and energy drinks than you can shake a stick at!
Viewing options for the 5km and 10km are quite limited (basically Epcot!), but then theyre short races so it's not really a problem. For the 1/2 and full marathon, its not really worth spectating near the start line. Its a bit out of the way and would make it difficult to get over to other places in time. The monorail runs between Epcot and Magic Kingdom, so once you head off to the start line, he can jump on that and see you at Mile 4 going into the Magic Kingdom and at Mile 8 coming out towards the Raceway. I wouldnt suggest actually going into the Magic Kingdom to spectate because its absolutely heaving in there and you'd more than likely miss him. Staying near the car park is definitely the best option.
After mile 8, spectating gets a bit tricky since the course heads out towards the arse-end of Disney World. Getting to places like the Wide World of Sports and Animal Kingdom is virtually impossible due to road closures. He'd probably be better off heading back to Epcot and either putting his feet up in the race retreat for an hour or so, or trying to head out towards the Yacht Club and Beach Club resorts to catch you around Mile 24. Or get a good seat in the stands and watch you cross the line.