+1
1. How much did you spend for that book? (Quoted from A Dictionary of English Collocations)

2. How much did you spend on that book? (My own sentence)

3. We spent many hours in a pleasant conversation? (Quoted from A Dictionary of English Collocations)

4. We spent many hours on a pleasant conversation? (My own sentence)

Are sentences #2 and #4 also acceptable?
+3
spend for a book - OK
spend on a book - OK. I use this more than spend for.
spend hours in conversation - OK.
spend hours on conversation - No!
spend hours on a project - OK. (working on a project)
spend hours reading - OK

CJ
+0
2 yes, 4 no, IMO.

3 means
involved in a conversation
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Comments  
http://forum.wordreference.com/threads/spend-money-on-for-something.1681431 /

As usual, the absence of context allows us to invent intentions for the speaker or writer, and from these inventions or assumptions flow our interpretations of the meaning of the sentence.

Here are some assumed intentions, and the resulting meanings of the sentence.

I think we should spend the money on a sports club with new gym and bar facilities.

Assume: A conversation among people trying to decide how to use the money from a bequest. Among the choices under discussion is a sports club. If the money is not spent on a sports club, it will be used for some other purpose.

Interpretation: "On" simple connects the money to an intended use. Let's spend it on this. If not, let's spend it on that.

On
points to the destination of the funds.
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I think we should spend the money for a sports club with new gym and bar facilities.

All of the above, both assumptions and interpretation, can be used again with for.

New assumption:
Money has been budgeted or allocated previously. It will be spent to create a sports club.

Interpretation: The sports facility should have, in the opinion of the speaker, a new gym and bar facilities. The speaker is advocating that the new sports club, in contrast with whatever facility it will replace, will have features not previously present.

The second assumption and interpretation might also work with on.

Conclusion: without more context and background, the two prepositions are interchangeable in this sentence. Neither one restricts the meaning. Money should be spent, according to the speaker. Either preposition can point at the use to which it should be put.
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I've just come across the question again whether spend has to be followed by on or whether it can also be followed by for. While doing my research, I realized that I have posted this question before (in this thread) and I've also come across this thread: http://forum.wordreference.com/showthread.php?t=2260356 In both cases the answer is that yes, for can be used as well (at least in the two sentences given in the two threads) and my partner, who is from the United States, also says that both on and for is possible. However, ABC of Common Grammatical Errors, which is based on British English, considers the following sentence as wrong: On St Valentine's Day some Japanese girls spend almost half their salary for chocolate. (sentence labelled as incorrect in ABC of Common Grammatical Errors) ABC of Common Grammatical Errors says that "[w]e spend a sum of money on the things we buy". Therefore, it should be: On St Valentine's Day some Japanese girls spend almost half their salary on chocolate. I now wonder whether in American English spend for is acceptable but not in British English.