Spark gets annoying when the material being sparked is not solid. My thoughts are that the properties of spark should take on its ctype. For example, sparked water still flows, falling brel falls, etc.c
If it doesn't break anything major, I wouldn't bother with a compatibility check.
The reason I haven't done this previously is because I suspect it would reintroduce this glitch (I can't remember if I ever actually tested whether it does though):
https://powdertoy.co.uk/Discussions/Thread/View.html?Thread=4709
https://github.com/FacialTurd/The-Powder-Toy/commit/13e90886c1d4ae571707c8f31a7702fce7b2ec74