For anyone reading, we hope this has been an informative discussion.
In short, Spark payments have a few important privacy nuances. Transactions that stay entirely within Spark, Spark-to-Spark, aren’t private and reveal a link between users. When two Spark users pay each other over Lightning, the connection on a Spark explorer is obscured, but timing analysis can still expose the receiver. If you send from your Spark wallet to an external Lightning wallet, Spark only has the same level of visibility as any other LSP. When receiving from an external Lightning wallet into Spark, Spark similarly knows only what an LSP would about the sender. However, the receiver isn’t completely private either, timing attacks can reveal the receiving address and wallet balance, making it less private than a standard Lightning receive.