Sportsbook Cash is for internal Sportsbook usage only. When I developed Sportsbook 10 years ago for XF 1.0.0, there were no points/cash/credits systems, so I needed something internally that could be used until an actual points/cash/credits type system was available. Sportsbook Cash is really only designed for INTERNAL TESTING. Its recommended not to use it, but instead, use an actual points/cash/credits system (like [th] Credits or DragonByte Credits (which IIRC, also has a sister addon that is a "store" that users can spend credits on stuff like you mentioned.
Its not all about SPENDING. For DECADES (with vBookie and Sportsbook), its a CONTEST to see who can accumulate the most MONEY (even tho the money is not real, its an addiction no different than those that wager in REAL LIFE, which is all about how much money won can win.
Just about every single community I've ever been a part of, its always been a contest to see who can accumulate the MOST "points" or "credits" or "cash". Its never been about "spending it", however, IF you use an EXTERNAL points/cash/credits system and that system (or a sub system) has features that let your members "purchase" things, then you have the best of both worlds (those that love accumulating can do so and those that are not even interested in sportsbook, can earn points doing other things and spend those credits/points/cash on things like buying an avatar lol).