I haven't done this breakfast since they started opening before 9 am, but we are eating here for breakfast for our current trip.
First, their breakfast is very good (fresh, tasty). However, while they have all the "basics," they don't really have any specialty items (like at Tusker or 1900 Park Fare, for instance). The lunch/dinner buffet is also very basic, but we didn't care for the food as much.
So, I think breakfast is better than lunch, and cheaper (if paying OOP).
As for the opening situation: here are the options. If you want to be the first into the park when they open at 8:30 or 8:45 (it apparently varies), you have to be there at 8:00 or so. If you get there at 8:30, you will be fairly back in the crowd to get it.
If you have an 8:00 adr, you'll be finished eating (and have seen the characters) by 8:45 or so. Then you can leave the restaurant and join the line to TSM or JTA. You won't be first in line, but you will still get a fairly early return time (and the time will be earlier than if you arrived at the entrance to HS at 8:30)
So, we're doing the breakfast (kids love Disney Jr). Also, as long as one adult is finished eating by 8:30 (very possible), they can go out and get at or very near the front of the line for TSM fastpasses, and meet the rest of your family outside of H&V, while the rest of the family does finish more leisurely.
Another tip: ask for your check as soon as you are seated and pay right away. This way, you won't have to wait for them to process your card while you are anxious go get going (everyone wants to leave around 8:45, and the wait to get your card processed and be a bit long, as so many are trying to pay at once). Once you get the card back, you can still wait to sign it until right before you leave (so you can adjust the tip based on quality of service).