I think the original post gave some very good examples of what can go between a the verb and object in the verb-subject structure.
To generalize, you can put something in between the verb-object structure to modify the verb, something to modify the object, or both. For simplicity's sake, let's call them adverb and adjective.
Using the original examples, you have:
发了愁, 了 modify the verb (let's call this adverb), you mean [发了]愁.
发个愁, 个 modify the object (let's call this adjective), you mean 发[个愁]
发过四次愁, 过 and 四次 modify the verb and object respectively, you mean [发过][四次愁]. 过 is serving as an adverb, and 四次 is serving as adjective.
You can only put adverb (compound structure that acts like an adverb is also being called an adverb here) directly behind the verb, and the adjective (like-wise for adjective) directly in front of the object. You cannot reverse this order. They also have to be adverbs that can naturally go behind a verb or adjectives that can naturally go in front of the adjective.
For example, you cannot put 正在 behind the verb.
However, you can say this:
The way to interpret that would be:
发 [[过][了]] [[无数次][大大小小的]] 愁.
verb adverb adjective subject/noun
The only addition to the above is that you can also add interrogatives that can come after a verb, and/or before a noun into the structure.
什么 can both go after a verb and it can come before a subject. So the second example can be interpreted in two different ways depending on context (why [are you] trouble? and what troubles [you]?).
I hope this helps.