There are several ways to track progress in the Play Sets & Infinity overall - such as Feats & Trophies, and with 3.0, the ranking titles. Since we've had the ability to generate sparks from the original launch, Infinity's use of Blue Sparks haven't made a whole lot of sense. I'd still like to see simpler controls for generating your own when you're designing your own game. I really liked the change in 2.0 that split the spark colors, purple for specials, green for healing, yellow for experience, & blue for "currency". There was even a Toy Box TV Hints & Tips video on creating a spark burst as a reward within a Toy Box. I'd still like to see a Spark Burst Creativi-Toy that could produce an explosion of a particular color, or a mix, with Locator toys support, to avoid combining some hidden Enemy Wave with a Trigger Area & Kill Switch.
If the Toy Box reboot would consider "dismantling" the Toy Store, and simply unlock sets of toys as part of the reboot storyline & instructional Toy Boxes, then the game designer could have the option to reset the Blue Spark count to 0, and add them back per the game design. Blue sparks could be the better currency for Tower Defense style games, where the in-game "Toy Store" (restricted edit ribbon) determines placed defenses. There would need to be a Properties update to choose them over Infinity coins, flowers, gems, etc. and of course the larger increment of purchase pricing. With the ability to reset them, and incrementally update them, Blue sparks could be another form of counter for Toy Box game displays & single-player Leaderboards. From an overall theming perspective, the notion of Blue Spark Count in Toy Box Game design just seems fun.
On a side-note, whether it's the original Counter toy, a Counter synched to Blue Sparks, a Scoreboard, or a Team Scoreboard, it would be cool to see Properties that could dynamically change a counter's multiplicative modifier, such as x2, x3, x5, x10, x1/2, and back to x1 (perhaps even to x-1) to make scoring games more interesting. The modifier would apply whenever the respective counter was incremented. Game designers could think up all sorts of ways for these various modifiers to come into play. It would improve lots of different types of Toy Box Games.
Given the existing mechanics of spark generation, I don't see Blue Sparks as XP; I see Blue Sparks as the symbol of recapturing the Imagination of the Toy Box, where the key to the story (& the business model) is to leverage the creative talents of the Disney Infinity Community.