I'm realizing I never returned to post my Spark results. Bottom line: much prefer the Fulltone Fat Boost 1. Despite the hype/advertising, the Spark had a "compressed" sound/feel to me whereas the Fat Boost sounds/feels more "open." Not a knock per se on the Spark - it may be perfect for your app - but wasn't what I was seeking. At this point, having A-B'd in person the Fat Boost 1 with several good boost pedals (or pedals that can be used for a boost), including the Earth Drive, I'm confident the Fat Boost 1 is for me and will not be searching further in this vein.
"For me, I think the only danger is being too much in love with guitar playing. The music is the most important thing, and the guitar is only the instrument." Jerry Garcia