The medicinal properties of lilacs have been documented since the middle ages. Used both in Eastern and Western cultures to lower fevers, aid in digestion, and as an anti-periodic (preventing the return of a disease). They also have many uses in skin care.
They lose the aroma during the dehydration process and really just don't taste great as a tea. One way to help with that is to use lilac infused honey. The honey absorbs the fresh floral notes and adds a lot of flavor to the tea.
I use 1 tbsp of tea with 1 tsp of honey (including the soaked flowers).