I love Seagrove. It's in the middle of 30-A corridor, so you don't have to drive too far to anything. It's close to Seaside but not as congested (except at the 395/30-A intersection in the summer, but off 30-A it's not congested), doesn't have the limited amount of beachfront properties that Watercolor does (most places in Watercolor are just too far to walk to the beach). I like the beach better than Grayton because you don't have to walk so far to get from the beginning of the sand to the water (that's a hike!). Eastern Lake in Seagrove has a nice outflow for kids to play in (as does Grayton), but it's not congested like Grayton and, again, not as long of a walk to the water.
Crossing 30-A: well, that's something you have to be careful about no matter where you stay in the area. But there are plenty of places south of 30-A, especially in the Eastern Lake Road area of Seaside (my neighborhood). It's all south of 30-A.
Seagrove has a Publix, plus a Tom Thumb if you really want to pick up a few grocery items fast.
Fast food doesn't exist on 30-A, but there is food that is fast. My feeling is that there's too much fast food at home; when I'm on vacation, I want something different.
Breakfast: we usually eat cereal at home, but we also like Amavida Coffee in Seagrove, Modica in Seaside (not too congested at breakfast time), and especially Hibiscus Café in Grayton -- like I said, nothing on 30-A is too far from Seagrove.
Brunch: Love the endless champagne brunch at Fire in Grayton, and like the brunch at Great Southern in Seaside.
Lunch: Seagrove Market Café, Flip-Flops, Bruno's pizza buffet, Cocoon's for sandwiches and prepared salads, etc., Red Bar in Grayton, Wild Olives in Rosemary.
Pizza: Bruno's, Pizza By The Sea, Angelina's, then there's our favorite, Amoré at Gulf Place -- again Seagrove is in the middle geographically so even that isn't too far.
Dinner: Any lunch or pizza place. There's a Goatfeathers in Seagrove for picking up fresh seafood and grilling an easy dinner at home. Then if you want to splurge, in Seagrove we have Café 30-A , plus not far from Bud & Alley's in Seaside or Borago in Grayton.
I prefer Seagrove to any area along 30-A after staying on many occasions all along 30-A while we were building our home.