Question: What's the difference between 许多 and 很多？

I have learned that 许多 can't be used as predicate yet in this sentence it seems to have a predicative function

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> 他觉得妻子虽然老了许多 但仍很美丽
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Answer: 
How about 恶趣味? Literally "an evil interest".

For your example,

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> For the renowned sushi chef, eating fish sticks drowned in tartar sauce was a guilty pleasure.
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> 对于一位有名望的寿司师傅，吃着配上塔塔酱的鱼柳条是种恶趣味。
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Some other interesting translations include:

* 罪快乐. It takes the pronunciation of 最快乐 (happiest) to imply that it's the happiest, yet a "crime".
* 罪乐感. It derives from 罪恶感 (guilt) to imply that it's a guilt which makes one "happy".
罪恶的快乐 or 带罪恶感的快乐

For example, 罪恶的快乐 is used in this article: <http://www.360doc.com/content/15/0301/14/11843203_451727066.shtml>

Compared to 罪恶的快感, I think 罪恶的快乐 is slightly less ambiguous. 带罪恶感的快乐 is not ambiguous but lengthy. In Chinese, shorter sentences are preferred. Some ambiguity can be resolved by context. A slight criticism is in Chinese, precision cannot be achieved without accepted gramatical tools (functional words).

罪恶的快感 = the pleasure of being guilty (similar to 完美犯罪的快感，快乐杀人)
For example: <http://blog.udn.com/godzillahome/20539898>

罪恶的快乐 = the pleasure mixed with some guilty feeling