So, 1625 is a solid spell. But there's some room for improvement that might also help to encourage more training in the 1600s. Just have some suggestions (most of which have been made before):
1) CS boost to spell infusion. Spell infusion is currently on the "Meh" side. Don't get me wrong- it's definitely in better shape than it was before. But being functionally stuck with 1602/1615 limits the potential. There's also a coinciding issue with Paladin 100's CS that needlessly limits a Paladin's hunting styles. What if spell infusing came with a significant CS bump? That would give the ability a lot more value, and if the bump were big enough it would expand the list of usable spells (doubling it!). I'm not really sure what the CS boost would need to be in order to make the 100s usable. But figuring that out would be a good starting point.
2) Adding 117 to the spell infusion options. This would also add some diversity to the ability- which is sorely needed.
3) Adding a bane option for the bonded weapon. Give it a component system and a tough skill check. Obviously no weighting, but flares and enchant could be options. Tie this to increased spell training- use it to push to 50 spell ranks or higher.
4) Give it a temp version that sanctifies a weapon or shield (For the caster only). Tie to increased spell ranks. (50 for temp weapon, 60 for temp shield)
5) Allow the Paladin to replace the plasma flares for guiding light with the flare type associated with their deity. (1625/1630)
6) Increase spell charges from scroll-based spell infusion. Instead of 1 invoke = 1 charge, allow training in summoning lore to increase it up to 1 invoke = 5 charges. Again, add some diversity here.
