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

> 
> 他觉得妻子虽然老了许多 但仍很美丽
> 
> 
>

Answer: 
How about 恶趣味? Literally "an evil interest".

For your example,

> 
> For the renowned sushi chef, eating fish sticks drowned in tartar sauce was a guilty pleasure.
> 
> 
> 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。
> 
> 
> 

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".
I found these on douban.com, maybe they are helpful.

* 偶尔纵欲
* 暗爽