In saucepan, combine sugar, eggs, lemon juice, and salt: cook and stir over medium heat until teperature reaches 160 and mixture is thickened (about 5-10 minutes). Cool completely. Cook spaghetti, drain and rinse in cold water. Place in large bowl. Drain pineapple, reserving juice. Pour juice over the spaghetti: stir in apple. Toss gently; drain. Stir in agg mixture and pineapple. Cover and refrigerate overnight.
Fold in whipped topping just before serving. Garnish with walnuts and cherries.