I'm another DLR regular who is returning to WDW for the first time since 2005. I did a lot of research to see if crowds are different on various days of the week, and here's a summary of what I found online:
- Locals go on the weekends, especially if there's a festival going. Epcot can get especially busy during the evenings on weekends as people come for dinner, while HS is busier mid-day on weekends. I saw a lot of "avoid MK on the weekends at all costs" posts.
- Most people go to MK for their first park of their trip, making it busier on weekends (especially Sunday) and Monday.
- Wait times are pretty consistent over the whole week at HS, with the biggest factor being if Rise goes down. If you're using G+ and ILL, HS can be do-able if you have a strategy.
- AK is the easiest park to handle when it's crowded, especially if you're willing to get there at rope drop, take an afternoon break, and then head back to the park in the evening after the crowds drop off. Note that it does close earlier than the other parks, however.
- Tuesday, Wednesday, and Thursday are the best days for all the parks.