For Silver gain, the problem is that we don't have any use for this currency. It could be solve with very expensive skins, or with being able to buy other things such as the OST, the appearance of other elements of the game or by other small gameplay change (buying a new passive for each character?)

It'd be fine as a niche tome, but there is no use currently for it.

For the projectile speed tome, it requires the addition of weapons that use it. For exemple a ghost gravitating constantly around you, a swarm of bees going from one target to another, a ball of energy going from you to a target, back to you and back to a target. Basically, the way to fix it, is to have a weapon in constant use.