You can use multiple devices on a single SPI bus, using several CS pins for selecting active slave chip. Display only needs to be updated once every 20ms or so, so SPI certainly can be shared. But I’m not sure the level of support of this in libDaisy, I’m not really using it myself.
@shensley probably has some suggestions for this. I recall that there were some plans to improve support for using UART/SPI/I2C for connecting custom hardware.