I can confirm this. I have Smiddi to level 99 and my heal other spell effects are increased although it is hard to tell with just 1 cast. However, after a few rounds of friend healing it became quite noticeable as he was restored to full hp and even I healed a bit from the 160-180 we both started with. More testing will likely be required to understand the full effect of the upgrade Thanks, I've added a note about it to the guide.