Some folks just aren't planners, and that's fine.
My counsel to folks visiting WDW in these days is the hassles you impose on yourself before you go result in a whole lot less hassles while at Disney. I'd much rather pace myself and do as much planning as possible in advance so that I'm hassle-free once on vacation. I hate being frustrated when I'm supposed to be having a good time.
It DOES make a difference to know in advance which park you're visiting. Some parks are more busy on certain weekdays than others ... morning Extra Magic Hours, for instance, make a huge impact on how crowded a park is, as do parades, special events, etc. If I can make a choice that determines whether I'm going to wait in line for a popular attraction for 90 minutes or 20 minutes, and I can do that a few months out, guess what I'm going to do. There are tons of good planning tools available ... I like the Unofficial Guide and Passporter. For the first time on our last trip, I checked on Tour Guide Mike (a DIS sponsor), and danged if there wasn't a BOATLOAD of helpful information there, and I thought I was pretty much in the know.
So, armed with that knowledge of what park I'm visiting, then I can go online, examine menus, poll the rest of my family/party, and determine where I want to have my TS meal on that particular park day. If you're in either the MK or Epcot, leaving the parks for a monorail resort or one of the Epcot resorts, respectively, just isn't that hard. For us, it's all about peace of mind.
Having said all THAT, you can certainly visit WDW and not worry about which park, which restaurant, or anything, and if you're willing to go with the flow, have a good enough time. CS spots aren't an issue, since they're walk-up anyway. Arriving at a TS spot in the parks just as soon as they open can sometimes work, especially in places like Marrakesh. Lunch TS spots are often available as early walkups in the resorts.
When all is said and done, do what makes you happy. The
Disney Dining Plan exists to serve ME, not the other way around. Don't serve IT.