I cannot speak to the online, premium version of roadfood. I bought the book a couple of years ago and found it useless for my needs. Six weeks on the road and not one place mentioned in the guide was anywhere close to where I was. It was interesting reading but **free**CH was the superior source of where to eat.
They lived in this area and so years ago they started off by reviewing many roadside eateries around this part of the state. I'm not nearly as fussy about food as many of the real hounds are, but I found that the Stearns fell in love a little too easily with their food finds, maybe for their uniqueness, but these finds too often turned out to be mediocre. I bought their book some years ago -- it was the "Diners, Drive-Ins and Dives" of its day and a fun read but not really a travel guide. Search CH for that.
I made good use of their first book on a vacation trip to Appalachia around 1990, finding things like biscuits and ham and peanut soup. In fact the waitress in one restaurant (in Virginia) recognized my source based on the items I ordered.
But out west, I rarely was close to cited places at meal time. But then the same applies to most Chow recommendations.
Still I do like the Roadfood segment on The Splendid Table.
I have not subscribed to the premium service, and haven't visited the site often in the past few years.
The "Where Should We Eat?" forum is devoted partly to exactly your situation. You can post your route and have Roadfood users offer suggestions. Chowhound has resisted this kind of board, preferring a regionally-based organization, but I've always thought a "route" board would be useful here. Roadfood.com users tend to be extremely friendly and helpful, but just as the Sterns tend to be easy graders, so do the users. I happen to find the boards there charming, and occasionally useful, but I prefer the thicker skinned Chowhound users.
Two observations about the Sterns:
1. I think that their background in art is part of the reason that they sometimes guide folks to charming places that look great (especially true of diners) but have only so-so food. I think they put more of a premium on ambiance and service in downscale restaurants than most CH's do, for better or worse.
2. You don't indicate how far you are going up the East Coast, but the Sterns themselves, if not the users, are particularly strong on Connecticut and to a slightly lesser extent, New England. If your trip finds you in these areas, you should read the Sterns' recommendations, even if you don't spring for the premium content.
I came upon Chowhound and Roadfood at the same time. Searching for regional specialties.
As already stated, they tend to like classic diners, B & Bs, inns, etc. There is also a premium on a single dish, rather than the entire menu. If you don't mind getting your sweetened ice tea at one place, driving 20 miles to get a pulled pork sandwich, and another 30 miles for coconut cream pie, then you will have a memorable meal.
I have found them useful for myself when searching for regional specialties and their eating tours. The Tamale Trail in Mississippi was great.