Sakaeyellow, your posts regarding the shared vocab of Chinese and Japanese is really enlightening. As a Malaysian Chinese who has brought up with Mandarin, I did not even realize that.
As for the general debacle regarding the relative easiness to learn a certain language, my personal belief is that it is totally
relative. We were brought up in different countries and have different backgrounds when it comes to language exposure.
As a general rule, Westerners may find it relatively harder to master pictographic languages (i.e. Hindi, Tamil, Chinese, Japanese, Thai) simply because of the fact that there are no alphabets involved, unlike the Romance languages. Conversely, it is also true that Asians may find it difficult to learn the Romance languages, simply because of the difficulties in pronounciation and the disparities between the enunciated sound and the written word.
However, I would like to clarify that it is definitely not true that Chinese speakers will master Japanese easier than non-Chinese speakers. While it is true that Kanji and Hanzi are similar, this is only true for the traditional form of Hanzi (fanti), which is not in use in China today. The simplified Hanzi used in China (jianti) is very different from both Hanzi and Kanji, for certain characters. Therefore, much confusion ensues for a Chinese speaker in learning Japanese, because he doesn't recognize a particular kanji at all; or it may be written with a different stroke count.
Hope this helps!