Consider TS lunches instead of dinners, you have a better chance of not waiting as long.
Be prepared to park hop; with only a few TS restaurants at MK, MGM and none at AK, EPCOT may be your best bet, or a resort TS.
Buffet style restaurants may have a shorter wait time due to the fact that patrons don't have to wait for wait staff nor do they wait for their meal to be prepared.
Check out the counter service menus at allearsnet.com and have plenty of back-up options ready. You may end up spending more time trying to find a TS or waiting around for a seat at a TS then you would if you had given up your spontenatity avoiding making ADRs. With so few choices in MK and MGM, and if you consider the possible number of tables in each restaurant, consider the number of guests in any given park in any given day, even if the ADR system didn't exist, the chances of you getting in a restaurant would be limited.

I made ADRs in advance of some places we ate last trip, and still waited over an hour for Cinderella's Castle, and over 30 minutes for Ohanas. As a walk up, we waited 70 mintues for Whispering Canyon at 9 pm. Now also consider that a great number of people made an ADR 180 days out, and that the ADR system is not really a reservation, but more like holding you a place in line until the people before you are finished eating, you may decide that TS without ADRs is more of a gamble and not worth your time. Have that CS list ready, so you have something to eat and when TS's spontaniously work for you, you can feel like you got an extra dose of pixie dust! My sister didn't make ADR's, and got frustrated at MGM when they couldn't find anywhere to eat, so they left for Downtown Disney, opting to miss Fantasmic...crazy!!!! Don't miss the parks and attractions for food! Eat CS and get TS when you can, and if you can't, go home after WDW and treat yourself to some really nice restaurants!
