I know, but we'll need to dedicate XP for that. The rewards of spending ~500 XP on the tech to get it ready for battle use aren't really very good at all. We could use the time required to train to 500 XP in a much better way.
And yet, you want to dump
more exp into the
very basic bunshin technique, rather than just go for the straight upgrade? I mean, really, that is an utter waste of XP, considering like I have
already mentioned, any experienced combatant is going to easily see through a basic bunshin no matter what due to the lack of shadow, lack of smell, lack of weight, lack of footprints, etc... And so, we'll
inevitably need to upgrade to better techniques in order to fight on the level expected of us.
Experienced Genin(Like Gai's team) will easily be able to handle the basic bunshin anyways, so I don't understand why you expect "adding" an element to such a basic, obvious, and easily avoided/ignored technique to be
better than simply going for the stronger clone techniques. At least Earth and Water Clones have a
physical presence, which makes it harder for people to differentiate between the clone and the actual person.
Yeah, but if that's the case all shinobi villages should be training high level courtesans for infiltration missions. Many spies in old times did that.
Again, this falls under the differences. But this time, between shinobi/civilian and home/mission. Shinobi know how to look for and read spies/enemy shinobi/"courtesans", so they'll have their guard up. But Minami/Mom is a civilian, so she's not a threat(
and she is a member of Konoha(Which is
home) with a kid as nin there), meaning he can let his guard down(But never truly down) around civvies. And then he was at home in Konoha with
tons of allied nins in the area, meaning his guard was further relaxed. If he was on a mission, far away and a girl/woman tried to do the same, he'd have his guard up to either ignore it or be suspicious of her.
Also, you're forgetting to take into account that any courtesans within Konoha are going to be thoroughly vetted for ties and spying and the like, plus they'd have to risk angry nins with chakra who are able to easily kill them when they'd have none themselves to defend themselves with(And before you point to Jiraya, remember, all the escorts that he met were
never at or in ninja villages). And any courtesans
with chakra will be promptly dragged into T&I to find out who they are, what ties they have to which village(s), why they even
have chakra, etc...
Far easier to do as Orochimaru did and just insert flunkies into the ninja corps, which only really worked as well as it did due to his prior knowledge of Konoha and how Sarutobi worked. Or do as Jiraiya does and simply rely on information from surrounding areas that
aren't the ninja capital of their respective lands.
Tl;dr: You're forgetting chakra, chakra sensors, chakra detection seals/spheres(See Pain throwing Animal Path into Konoha), and it throws everything out of wack. So courtesan training for spies wouldn't work. And as for Ibiki, he was on home ground, amongst fellow nins, confronted by a civilian that he could easily kill within seconds of she actually meant any threat to his life(somehow), so his guard was simply down.