This is perhaps going to sound very niggly, so I apologize in advance.
For your first sentence there, without the word "on" between "money" and "buying", it (can) sound like the money was spent in the process of going or being somewhere to buy books. The "on" would help show us specifically what the money was being spent on - i.e., the books rather than something else associated with buyi
Sorry, Jason, but "He spent a lot of money on buying books" sounds odd to me. I would prefer either the original ("He spent a lot of money buying books") or simply "He spent a lot of money on books." (We would assume that the money was spent buying the books rather than, say, taking them out to dinner and the theater. If the sentence said "He spent a lot of money on women," the supposition wou
Now that you mention it, it does perhaps sound odd like that - but is it because of the grammar or the potential redundancy of the lexis? When I thought about it, it was the occurence of "spend" and "buy" together that made it feel odd to me.
I hope others can dip into this and help me with clarifying it, too.
For example, I feel pretty sure that if you mention an indirect object