Hello we are going 24th September 2018 for 21 nights. The upgrade cost is around 580. Are the table service restaurants worth the upgrade? I know they seat you but do you get a choice where? Thanks for all your help.
Generally, no choice where you sit (though, you can always make a request, and they will try to honor it, if they can, but no guarantees.
As to whether they are worth the upgrade depends on what you like to eat, and where you end up eating. Some TS restaurants only cost a few dollars more than a QS restaurant (such as Plaza restaurant, Sci Fi diner), some cost a LOT more (such as Akershus, Fantasmic dining packages).
Disneyworld.com has a listing of all the restaurants, both QS and TS. Take a look at the menus and prices. Decide then if these restaurants appeal to you. With 21 nights, you would get 21 credits. Some restaurants ("signature restaurants"), and the dinner shows, require 2 credits. This info is available online also. With so many credits, and it being your honeymoon, I would absolutely look into some special dinners!
If you do get the dining plan, you want to make your reservations for the first 11 days of your trip at exactly 180 days before check in, as some of the most popular restaurants book up before 180 days! After that, each morning you'll be able to make reservations for one more day (a rolling 180+10 day booking window).
Are you in the US? If so, you can only book a package (dining plans result in it being a package, even if you get your tickets elsewhere) for 14 (maybe 15?) nights. However, you can book back to back reservations, and add the dining plan to both. I don't know if this applies to those from outside the US.