Mass Haste, Protection from Spells ...

[Cihparg]

The suggestion is: Include NEUTRAL people to the target list, instead of just PARTY.
There is probably other spells that could use this as well, but this is just to name a few.

Yes, this could also be inconvenient; you could end up casting a spell on someone who finds all magic hostile.
But it's still much less inconvenient than asking a group of people to invite you, just so you can cast a spell on them, and then ditch their party.