You can make C.H.I.P into an airplay receiver (or DLNA) . This was the cheapest option I was able to figure out for doing this, and while I'd use e.g. a Chromecast audio if I could, it can't replicate the functionality I want. Namely, to use my phone as a remote control for my home audio system, not a streaming source.

I've also made some nice, tactile (e.g. big switches and clicky knobs) electronics for simple things like kitchen timers, etc. with Arduino style boards.

It sounds like you shouldn't buy any more of them, though. If you're not inspired to make something, more boards certainly won't help that.