IMO the answer depends partly on whether there are other good options for curing those moodlets. For example, showers are good for anything that singes a Sim, but the rest of your list may have a greater need for your charm's help.
You'll probably also want it to cure out the Pestilence moodlet (since that's the paired spell to the charm) and Dark Slumber (since that's from eating a witch's poison apple). I would also say removing the Mummy's Curse from WA. I guess this depends- do you want the charm to be a healing spell or do you want the witch to be channeling sunlight? The healing spell would be more powerful. The other option is less powerful, and much of what it would deal with comes from Seasons, but gives the spell a theme.
I don't have all the expansions/store items, so this if going off a list of moodlets (which means I will have missed some possibilities). In addition to the ones you listed-
Sunlight possibility one (the charm is a healing spell):
Too Spicy (SN)
Food Poisoning (LN)
Allergy Haze (Seasons)
Nauseous / Herb Nausea (Uni)/ Time Paradox Sickness (ITF)
Aching Back/ Sore
Hurt Hand (WA)
Hurt Foot (Pets)
Cat Scratch! (Pets)
Saddle Sore (Pets)
Mosquito Bite (IP)
Sea Sick (IP)
Ouch My Face (WA)
This probably shouldn't have vampires get the 'Too Much Sun' moodlet
Possibility two (the charm is actually you channeling sunlight into them)
Brain Freeze (Pets/Seasons)
Monsters Under the Bed (SN)
Nightmare (Generations) and Gnightmare (Seasons)
Knocked Out (WA/ Amb./SN)
Starting to Shiver/ Teeth Chattering/ Frostbitten (Seasons)
Frosty Face (Seasons)
Once Bitten, Twice Shy (SN)
Along with the vampire's 'Too Much Sun', you may want to have it give the 'Plagued by Nature' (for sims with Hates the Outdoors) and 'It's Too Early' (Night Owl).
On the up side, it could give 'One with Nature' (Loves the Outdoors- or maybe everyone except people with Hates the Outdoors) or 'Suntanned' from Seasons.