Katakana Analysis Final!

Hello, everyone!

A couple of weeks or so ago, I posted a Katakana Analysis Draft as part of my class Katakana project.  Now, I am back to finish the project off!
First, 私のブログで コメントをポーストした日本語の四年生と五年生、どうもありがとうございます！Thank you to all of the fourth and fifth year Japanese students who posted on my blog!  Your comments and feedback are gratefully appreciated!
With the comments and feedback from both the older year students and from discussions in class in hand, I am ready to finalize my Katakana Analysis Project!  Below, I have posted the analysis of my two original Katakana samples with additional information.  Please enjoy!

The first is from a McDonald's campaign.  I realize now that it probably (or maybe hopefully is a better word) is not actually a real-live McDonald's campaign; perhaps it is some sort of rendering, as one may find on DeviantArt.

Humbly borrowed from tofugu.com at:

http://www.tofugu.com/wp-content/uploads/2008/11/01_imlovinit.jpg.

Disturbing image of Ronald McDonald aside, the well-known English slogan for McDonald's, which is "I'm Loving It," is written in katakana on the right. These are clearly loanwords that come directly from another language, and the purpose of subscribing these particular words in katakana was so that Japanese speakers would be able to understand.
But I cannot help but wonder - do they actually understand? These three words, when spoken, are actually still just English words. Even if they are in katakana, would a Japanese speaker who knows no English and does not recognize the slogan be able to understand what he or she has read? In such a case, the katakana would have no more meaning to the readers than if someone had written "I'm Loving It" in English from the start.
Perhaps, then, native Japanese speakers would be able to at least somewhat comprehend the foreign phrase by association.  If someone sat down to watch a McDonald's commercial, and saw how happy the people were acting as they chewed on their burgers and fries, and then they heard or saw the expression 'I'm Loving It,' katakana or otherwise, written down the side of a television commercial, they would probably be able to associate 'I'm Loving It' with the happy actors and their portrayed enjoyment.  But would that association be enough?  That is the question that advertisement companies targeting foreign parties must ask.


I also found this amusing sample of Japanese onomatopoeia.

Humbly borrowed from bushtalk.blogspot.com at:

http://www.tjf.or.jp/eng/content/japaneseculture/images/tb_no13/t13_28.gif

Onomatopoeia are used to, basically, portray 'sound effects.' So to write onomatopoeias in katakana is doubly effective, because the reader then sounds out the katakana and can hear or feel the sound that the onomatopoeia is intended to represent.
Both anime and manga tend to use katakana-written onomatopoeias very liberally, and I've noticed that the way the katakana are presented can help with conveying the onomatopoeia's intended sound. For instance, pikapika for 'shine' or 'brightness' may be written in small, bubbly letters, while nyanya for a cat may be written in a long, curling line. The extra aesthetics help get the point across.
In the above picture, though, there is still another way of adding a different flair to onomatopoeia.  Notice how two of the samples are not written in katakana at all (as in, ざわざわ and どきっ are written in hiragana).  Why could that be?
To me, it seems that the katakana written in hiragana automatically have a bit of a softer look than those written in katakana.  Furthermore, the katakana expressions seem scratchier, and maybe a little more unnerving as well (just a little).  The difference between the two add another layer of dimension to these outgoing expressions.

The above examples are just two instances in which katakana are used in the Japanese writing system, but there are, of course, far more. The different applications, and methods of application, are so wide, and so varied, that even native Japanese speakers seem to have trouble capturing the essence of katakana usage easily in a simple one-sentence definition.
Textbooks have tried to do so, but their answers seem to be vague, and each textbook may place more importance on one function of katakana than another. But, typically, the textbooks divide katakana usage into three categories: for loanwords, for onomatopoeia, and for emphasis. This categorization covers a very large range of possible usage of katakana in the simplest way; no doubt, that is why the textbooks classify them so.
As textbooks, perhaps that is the best that they can do in describing katakana, by speaking of them in such a vague, simple way. But, from my analysis, it seems that katakana has far more meaning as a complex part of Japanese culture - something that textbooks would no doubt have trouble to truly explain.