In a medium bowl, whisk the mayonnaise and cream cheese until smooth. Mix in the cheddar, Gouda, pimientos and their liquid, scallions, 2 tbsp. parsley, the paprika, cayenne and garlic powder; season with salt and pepper. Cover and chill up to 1 day.
Garnish the dip with more chopped parsley and serve with the vegetables and crackers for dipping.