Cook spaghetti, with 1 tablespoon salt added to water, according to package directions; add sweet corn during the last 3 minutes of pasta cooking time. Use tongs to transfer ears of corn to cutting board. (If using frozen corn, drain with pasta.) Drain spaghetti; rinse in cold water and drain well.
Cool corn until easy to handle. Hold corn upright. With fingers away from knife blade and cutting down the length of the corn cob, cut off corn in planks.
In large serving bowl combine cooled drained spaghetti, cucumber, squash, onion, celery, and sweet pepper.
In jar combine vinegar, oil, sugar, dry mustard, celery seeds, and 1/2 teaspoon salt. Cover; shake well to combine and dissolve sugar. Pour over spaghetti mixture; toss to coat. Gently fold in corn planks. Serve immediately or cover and refrigerate up to 24 hours. Makes 8 servings.