People often have a problem with Deism's refusal to answer speculative questions. The one most usually asked is "Why would God create the universe and then leave it alone?". Many Deists struggle with answering this objection, so now is as good a time as any to bring it up and talk about it. It is one of the most important topics within and outside Deism.
I doubt anyone considers the question to be vain itself. It is common and normal to try to speculate about this sort of thing. After all, who wouldn't like to know the ultimate purpose of everything. However, that we can pose a question doesn't necessarily mean that we are going to be able to answer the question. There is nothing that precludes a specific question from being unknowable, and it is a possibility. I contend that attempting to analyze the will of God can only be a speculative endeavor due to it being unknowable.
The reason that I contend so is because the topic is an antinomy. I use antinomy in the Kantian sense here of two possible conclusions which we cannot distinguish between by the use of pure reason. On the topic of God's will, the two conflicting questions posed are "Why would God create the universe and then leave it alone?" and "Why would God create the universe and then meddle in it?". Each of these questions seem equally valid to me, and any attempt to answer either of them could only be speculative or faith-based. This shouldn't dissuade anyone from being speculative about it, but I'd strictly warn against trying to make a universal argument in either direction. Stick to what can be proven via philosophical inquiry.
It should be noted that by proposing this antinomy, I am not claiming that contradictions can exist. Antinomies only show that we lack sufficient information to deduce an answer from what can be known. Antinomies do not claim to show that both possibilities can occur. This becomes simpler if we think of them in more familiar terms. For example, I could either eat breakfast tomorrow or skip breakfast tomorrow. Either choice isn't incoherent by themselves. I could do either one. Therefore, attempting to determine a priori what I will do tomorrow in the absence of other information is an antinomy. It does not mean however, that I could eat and skip breakfast on the same day.
Antinomies are important because they demonstrate the theoretical limits of philosophical inquiry. It is important to be aware of these limitations because trying to transcend them will lead to error and to fallacy. There is no wisdom in attempting to make up an answer to something which we cannot answer. Pandeism was an attempt to answer this antinomy, but it struggles with issues about how God could become the Universe and trying to maintaining coherence. It would be wiser to understand that some questions cannot be answered.
In conclusion, when constructing a worldview, do not start by trying to fit in what you think is true into the truth. Our minds are notoriously good at tricking ourselves, and not placing careful limits on the method by which we determine truths will lead to error. In a case such as this one, it is important to distinguish arguments from necessity and contingent arguments. In an antinomy, we may have two conflicting contingent arguments but cannot have a necessary argument. Unless such a necessary argument is demonstrated for the will of God on sound premises and via valid deduction, I do not consider the matter to be solved. I consider it to be necessarily unsolved.