Well, yes ... he attack, since you are halfling, but you are not Gibblebog (or what his name was :-/) ...
But you avoided one diceroll, and suceed.
With Sazza, she is still a goblin ... you would need to discuise her, wich as far as i know is not possible (at least yet). :-/
About that ritual statue ... im affraid i miss your point, why would anyone care that you were Gith? Statue is gone, druids have no reason to steal it ... therefore it had to be outsiders. O_o
Also there is one more use that i know of but...
when you reach Githyanki patrol, only way to suceed in that conversation and avoid fight is being Githyanki ... that is teoreticaly, i didnt try it yet.
Read Mind on the other hand is quite usefull, i mostly used it in goblin camp ... but there was some, maybe not so many, but certainly some ways to use it to avoid combat.
I dont think that this cutscene is good idea ... in that case every conversation shall take double, or triple time, untill you choose with every spell that can be used in coversation if you want or want not use it.

But! I second that there certainly should be options on crittical moments for player to use certain spells during conversations ... but i would like to also see NPC (at least have chance) to noticing that player is casting some spell. Simmilar to when NPC is using spell on you.