Not quite a senior (although AARP may beg to differ!), but definitely a baby boomer! And, sadly, won't be any where near WDW before December, 2011. *sob*
You'll find massive changes since 1979! I had 22 years between my first visit to WDW in 1981 and the second in 2003. It went from a few resorts, convention center, one park and one park under construction to about 20 resorts, four parks and two water parks! Plus two miniature golf courses!
Some suggestions:
If you have some free time, take a tour of the monorail resorts (GF, Polynesian, CR) or a Friendship boat tour of the EPCOT resorts (BWI, BC, YC, S/D. You can combine the tours with a meal (ADRs most likely needed) or perhaps visit a lounge or six!

It's also possible to visit WL and Fort Wilderness using a boat from the MK docks--makes a nice change of pace.
Strolling through DTD (Downtown Disney) can be nice. I'm not much of a shopper, but do enjoy wandering through it at least once each trip. You also can take a ferry from DTD to POFQ/POR and OKW and SSR. The Turf Grill at SSR is a nice place for lunch (probably dinner, as well, but can vouch for lunch there) and can be combined nicely with time at DTD or touring the other resorts.
Magic Kingdom: Nice job booking the KTTK tour, BTW. It's a terrific tour! You'll find yourself looking at MK a little differently--perhaps with even more appreciation--after the tour!

Mickey's Philharmagic is a must. It's an indoor show--air conditioning! The river boat is nice, as well, even if it is a ride! Hall of the Presidents (haven't seen it recently--we always seem to miss it) is an audioanimatronics show. Plan lunch at Columbia Harbour House, which is nearby. The three o'clock parade (3 p.m. on Main Street!) and SpectroMagic and fireworks (still Wishes?) some evenings (check the schedule). If you happen to be around the Seven Seas Lagoon at the right time, you also might catch a glimpse of the Electric Water Pageant. It also can be viewed from the GF, PR, CR--and possibly Fort Wilderness or Wilderness Lodge. Can't remember at the moment. It's short, so I wouldn't schedule around it.
EPCOT: As others mentioned, there is a lot to do here without ever going on a ride! Soarin' is terrific, though. If you plan to ride, get a fast pass early in the morning. Return time will be late afternoon. And Spaceship Earth! It's inside the signature geodesic sphere in Future World. Very gentle ride. Illuminations: Reflections of Earth is the evening finale here. Find a spot upwind around the World Showcase Lagoon and enjoy the show. May not be shown every night (used to be), so check the schedule.
Animal Kingdom: The Lion King show (can't remember the correct title at the moment) is a must for me. It has been enclosed and is air conditioned now--it wasn't in 2003! The Finding Nemo show also is supposed to be terrific--haven't seen it yet. Both are live shows. This is a difficult park for me to navigate--the uneven terrain plays havoc with my old foot/leg injuries, so others can provide better pointers than I can. I do love the afternoon parade at this park.

Apparently, the park is open some evenings now, so that may be something to explore, as well.
Disney Hollywood Studios: Beauty and the Beast show is one of my favourites. You also might enjoy The Great Movie Ride. A bit hokey, but fun if you have the right spirit. The animation studio is a must--be sure to stay to learn to draw a Disney character after the show! There are other live shows toward the back of the park: Lights, Motors, Action and Indiana Jones. The last show of LMA is around 3 or 4 pm--check the park schedule. Fantasmic! is the evening finale, although no longer shown every night. Check the schedule. If you don't have a Fantasmic Dining Package, plan to arrive 30 to 60 minutes before the start of the show to get a seat. Unless you have someone very tall or wearing a large hat (ask him/her to remove the hat during the show) in front of you, all of the seats provide a good view. You can bring food & beverages into the amphitheatre, if you like, or purchase some at a very busy concession stand in the rear of the theatre.
You'll notice I say "check the schedule" regularly. It's a good idea to plan your TS dining (if any) and park days around the parades and spectaculars, if they are important to you. Most were shown daily at one time; now they are offered on a more limited basis. The park hours for May should be posted soon, it they aren't already available.
What ever you do, relax and enjoy your WDW holiday!
