How close will the spirea be to the spruce? You might find that the spirea is fighting the spruce for nutrients and moisture if planted too close. So, what spirea are you thinking about planting? Sundrop with its golden leaves would be so pretty combined with a blue spruce. Or, the pink flowers of Superstar with a blue spruce!
WILL SPIREA GROW WELL IN ACIDIC SOIL NEXT TO A BLUE SPRUCE?
The soil should be fine. A bigger concern is root competition.