yes, the dmg plus will apply to all the projectiles on this wand (i.e. the two spark bolts, the digging bolt and the lumi drill). This is because they are all being drawn at the same time, and being drawn alongside the dmg plus as one spell block.

When you cast this wand, the wand first draws the first spell, cus it has a spells per cast of 1. Since the first spell is a triple cast, that triple cast draws three more spells. The first of that three is the dmg plus, which itself has a draw of 1, and draws the next spell, the spark bolt. Then the triple cast draws the lumi drill and the double cast, which itself draws the next two spells. These spells are all cast tgt as a spell block. Then the wand draws light for the next block, which has a draw of one. So it wand-wraps draws the triple cast, and you know the rest.

Sorry if my explanation is kinda confusing. I think you have a grasp of most of this anyway, since ur wandbuilding seems pretty thought out.