Can anyone provide some insight into the differences between 想 (xiǎng) and 想要 (xiǎng yào)?

I've been told (in Taiwan) that it's much better to use 想要 (xiǎng yào) when you "would like / want" something, and that 想 (xiǎng) doesn't really make a lot of sense on its own.  But I see 想 often on CPod and other Mainland sources.

I've also been told that using 要 (yào) to ask for something in Taiwan is rude, and that you should always use 想要 (xiǎng yào).

Any insights would be appreciated.  Thanks.

Traditional Chinese Version:

When you want to buy book in the book shop, you can use the following words:

你好　Hello

想　　want

買　　Buy

書　　Book

多少　how much / how many

元　　dollars

錢　　money

例子example:

Q:你好，我想買這本書，請問多少錢？

Q:Hello, I want to buy this book, how much is it?

A:三十元

A:Thirty dollars.

Note:

In the example, 本 is the quantifier of the book. 1本書,2本書,3本書...

請問 means "may I ask". It can be cancel in the sentence. But it is more polite if you use 請問 to ask question.

Simplified  Chinese Version:

When you want to buy book in the book shop, you can use the following words:

你好　Hello

想　　want

买　　Buy

书　　Book

多少　how much / how many

元　　dollars

钱　　money

例子example:

Q:你好，我想买这本书，请问多少钱？

Q:Hello, I want to buy this book, how much is it?

A:三十元

A:Thirty dollars.

Note:

In the example, 本 is the quantifier of the book. 1本书,2本书,3本书...

请问 means "may I ask". It can be cancel in the sentence. But it is more polite if you use 请问 to ask question.

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I come from China Hong Kong. My mother language is not Chinese, it's Cantonese. But in wiriting, they are same.

Anyway, I am not good English. If you find any mistake in the text, please tell me. I want to improve my English and improve your Chinese! =]