We've gone in September without the dinner package and been able to get decent seats. We just grab something to go and eat in the theater before the show starts. If you have small children I'd bring something to entertain them with.
Sounds like you're going during an off time and should be fine without dinner package.
We also went during an off peak time (early May) but did the package only because we love Mama Melrose and planned on dinner there anyway. If you plan on dinner at MGM, might as well book it, otherwise, you're probably just fine.
We were at WDW in October last year. We saw Fantasmic on Sunday, 27th. We didn't get the pkg and got there about 45 minutes prior to the show. Although we didn't sit in the middle section, we were in the Pocahonta's (spelling?) which is not bad.