For the Crust: Adjust oven rack to middle position and preheat oven to 350°F.
Combine cracker crumbs, melted butter, brown sugar, salt, cinnamon, and cloves in small bowl, stirring until crumbs are thoroughly saturated with butter. (Alternatively, process cookies in food processor and add remaining ingredients, pulsing until well combined).
Press onto bottom and up sides of 9-inch springform pan, leaving about 1/2 inch from top of pan. Line exterior of pan with foil.
Bake crust until golden, 10 to 12 minutes. Transfer to cooling rack and cool completely, 15 to 20 minutes.
For the Filling: Place clean kitchen towel in roasting pan. Set tea kettle or pot of water to boil.
In bowl of standing mixer or large bowl, whip egg whites and salt with whisk attachment on medium speed until soft peaks form, about 2 minutes. Gradually add 1/2 cup sugar and continue whipping until stiff peaks form, 1 to 2 minutes longer. If you used the stand mixer bowl, transfer whites to separate bowl.
With paddle attachment, beat cream cheese, remaining 1/2 cup sugar, and egg yolks on medium speed until smooth, about 2 minutes. Add the flour and orange zest and beat until fully incorporated, about 30 seconds. Add the pumpkin purée, sour cream, vanilla, cinnamon, ginger, and cloves and continue beating until creamy and smooth, about 2 minutes longer, scraping down sides and bottom of bowl with rubber spatula as necessary.
Stir 1/3 of egg whites into cream cheese mixture, then, gently fold in remaining egg whites.
Scrape batter into cooled crust and place in prepared roasting pan. Pour hot water into pan. Bake until cheesecake is set but still a bit wobbly in the center, 75 to 90 minutes. Transfer roasting pan to cooling rack and allow cheesecake to sit in pan 30 minutes.
Transfer cheesecake directly to cooling rack and cool completely in pan, 1 to 2 hours. Transfer cheesecake until completely chilled and set, at least 3 hours.
For the Spiced Walnuts and Assembly: While the cheesecake cools, adjust oven rack to middle position and preheat oven to 300°F. Line baking sheet with parchment paper.
Whisk egg white, orange juice, and salt in medium bowl. Add nuts and toss to coat. Transfer to colander and allow to drain, about 5 minutes.
Combine sugar, cinnamon, ginger, and clove in second medium bowl. Add nuts and toss to coat. Arrange in single layer on prepared baking sheet and bake until crisp, 30 to 40 minutes.
Transfer to cooling rack and cool completely, about 30 minutes. Break nuts apart and coarsely chop.
Heat syrup in microwave for 20 seconds. Brush over cooled cheesecake and sprinkle with nuts.