Grapes are incredibly high in sugar, broccoli has a fair amount of carbs as well, though not nearly comparable. If you're insulin sensitive like me you can have these foods, but only in small quantities/portion appropriate servings and always with a food that slows their digestion. If you're looking for fibrous foods to add bulk to your meals the Atkins Induction veggie list, especially the salad veggies, would be the place to look. Four or six stalks of celery dipped in hot sauce or a dressing is an excellent snack with fairly high satiety properties for the calories spent. A salad of mushroom, cucumber, green onion, cherry tomatoes, and bell pepper can give you such nutritional bang for the buck - on almost ANY plan. Add some meat and cheese to that and you have a filling, awesome meal for comparably few calories and low glycemic load.
Try not to play diet tricks on yourself. Free foods are the epitome of diet tricks, as though eating a box of snackwells or five grapefruits should still count as on plan
Even free and diet foods benefit from being portioned out. Eat a second portion if you're still hungry, sure, but don't lose track of what is and isn't sensible eating just because a diet has a loophole for it.
Lots of high fiber foods you can enjoy, just don't overdo it, especially on fruit.