Little comments and other stuff:
(snip)

Remember that this Ranma has had a girl's body for several months and
that he's proved to be pretty much unaffected about seeing Akane
and Shampoo naked and very close to (or practically clinging to)
him in that state, so it's pretty unlikely that seeing a little skin
would affect him that much

This actually is incorrect. At the end of the first beach
episodes (Phoenix Pill) Ranma faints and nosebleeds when
Shampoo glomps him in the bath. So he was aroused.

One time of how many, I didn't care to comment that

I've always maintained, in my own mind at least, that Ranma's lack of
reaction to the sight of a naked girl was due to self preservation.  Ranma
is (in many ways) his father's son, and hence he'd hide/stifle/deny any
sexual urges he felt whenever seeing (or getting touched by) Shampoo's,
Ukyou's, and Akane's naked forms to avoid severe trouble.  Given Akane's
explosive reaction whenever she caught him in a compromising position with a
girl, I think it highly likely that his body and mind adopted sexual
neutrality as a survival technique.

I disagree. More likely, he simply didn't care. Besides, he's quite
used to seeing nude females (well, one nude female). Contrast with
Ryoga who does teh faint+nosebleed at each opportunity.
In essence, Ranko being so similar to his female form, it should be
the one least exciting female in his new world.

I acree to some excent of both comments: seeing his (hers?) own body *has*
very likely made Ranma at least more resistant to feminine charms than
normal person and given that permanent thread of getting globbered had
propably rised it even more. 
Besides on 'Careful Destiny' Part two he says to Ranko (when carrying her to
Dr Tofu): 'In fact it hardly ever crossed my mind.' So there, remember what
you have wrote yourself (heh heh, cotcha)

(snippo)

(besides he has seen Ranko in much lesser for several times without
being affected, at least more than physical level). Now, I'm not
saying that this shouldn't affect him , at least somewhat (they say
that seeing little bit can affect you more than seeing it all.  Go
figure!), but hardly to this level.

On the other hand, the mood of the previous scenes was far less
inciting to any lewd thoughts. remember, also, that Japanese are
more casual about nudity, so nudity in and of itself is not
this arousing to somebody who's seen it all so many times.
On the other hand, Ranko's situation, being helpless and very
unlike her tomboyish self, and also aving been recently
aroused herself, would explain the difference.

Well, I know that seeing a woman in lingerie arouses my interests far more
quickly than seeing the same woman completely nude.  The expectation of what
might lurk beneath the clothes adds to the attraction for me.  And hence, I
assumed that it would be the same for Ranma.

Hey, the POINT is that Ranma WAS affected (he got erection) when seeing
Ranko practically naked (hell, who wouldn't be), and that I'm not so much
critisasing his reaction as it's strenght (read last sestence more carefully
and note this)on second time. 

Well, that's of my hands now.
KK