For tea: In a small saucepan bring the water to boiling. Add 1/2 cup hibiscus flowers. Reduce heat; simmer, uncovered, 5 minutes. Remove from heat; steep 10 minutes. Strain through a fine-mesh strainer, discarding hibiscus flowers; let cool.
Meanwhile, in a spice grinder process remaining 1/4 cup hibiscus flowers until finely ground. Combine with 1/4 cup sugar and pinch salt; place on a small plate.
Return cooled hibiscus tea to saucepan; add remaining 1/4 cup sugar. Cook over medium-high heat until reduced to 1/2 cup, about 15 minutes. Remove from heat; cool completely.
To serve, moisten rim of each glass with a lime wedge; wiggle rim in hibiscus-sugar mixture to coat completely. Divide cooled hibiscus syrup among glasses. Top with sparkling wine. Serve immediately.