Thank you Nikulas for reminding me of this answer from the past. After reading it, I decided to do a couple minor edits by highlighting two key points within my answer.

I am starting to discover that desire is actually counterproductive to manifestation. Desire has its own value and purpose, but in the application of the law of attraction it actually keeps your manifestation away from you. The greater the desire it seems, the greater the distance between you and the manifestation of that desire.

Let me try & break down my understanding of this phenomenon as follows.

The most appropriate use of desire, it seems, is to use it as a pointer towards your joy or excitement. You can imagine it like a sign post pointing out your greatest joy available at your present point of reference, & manifestation from an unlimited potential available to you at all times. But that is the extent of its beneficial application with regards to manifestation.

When it comes to manifesting your desire there is a catch 22 relationship with desire & manifestation. Desire represents something that you want & something that you don't yet have. This is why you desire it. If you already had that thing you wouldn't desire it.

Imagine it this way. Have you seen someone who just won the lottery having the desire to be wealthy? No. why not? Because it is no longer a desire, it has manifested. Well how about health? Have you seen someone who is already healthy having an intense desire to be healthy? Well I haven't. I have found that only a person who is sick, or someone who believes that they don't have health, will have an intense desire to be healthy.

So desire doesn't represent the experience of "having" something. It actually reinforces the not-having of something, therefore the desire to have it.

The next factor & perhaps the most important key factor in manifestation is the moment of "now". Also known as the eternal now moment. We exist only within the moment of now. Our entire lifetime unfolds within the moment of now.

When we envision an experience we desire, it has to be held in consciousness within the moment of "now" if you want to have any chance of experiencing that desire. Why? Because it is the only moment in which our existence actually happens.

So therein lies the paradox. The strong desire reinforces the Not having of something & if you imagine having your desire, "which you don't have yet", you tend to imagine having it in the future which doesn't exist because only Now exists.

So you have to take your desire & intently daydream "or live the moment" of already having it in the "now moment". You must never imagine it in the future or "desire having it". It should be "thank you God for providing this experience" & intently feel that power of faith in living in that moment as-if God has already provided it for you.

I think greater desire would cause the manifestation to occur quicker, provided the feeling behind it is positive. However if the desire is great but the feeling behind it is coming from need or desperation, it would hold the desire further away because the feeling would be on the same frequency as the absence of the desire.

Here I have a question that answers it. http://www.inwardquest.com/questions/1104/what-is-the-process-of-manifestation.

Wanting is ok. Faith that it is yours and on it's way must accompany your desire. It's the "I don't want" thoughts that are detrimental to your desires.