There is no such thing as intrinsic value.
All value exists as a relationship between states of affairs and desires. If an agent A has a desire-as-end that P, then any state of affairs S in which P is true has value to S.
This is the only way in which something has value.
Desire fulfillment does not have intrinsic value. In order for desire fulfillment there must an agent A that has a desire-as-end that P where P = "that there is desire fulfillment". To this agent, any state of affairs S where P is true has value to that agent (the agent has a reason to act to realize such a state). However, that state of affairs S has no value independent of such a desire.
We can illustrate this by imagining two universes.
In Universe 1, there is an agent named Abel. Abel has a desire that life exists. Furthermore, in addition to Abel, there is a planet on which a very primative form of life exists.
In Universe 2, there is a planet on which a very primative form of life exists. Abel does not exist, nor does his desire that such a planet exist.
The thesis that desire fulfillment has intrinsic value implies that Universe 1 has intrinsic value while Universe 2 does not. Universe 1 has desire fulfillment - an agent with a desire that P and a state of affairs in which P is true. Universe 2 has no desire fulfillment. It has a state of affairs in which P is true, but no desire that P.
So, the thesis that desire fulfillment has intrinsic value says to choose Universe 1.
Desirism states that desire fulfillment has no intrinsic value. The only choice that it makes any sense to talk about is Abel's choice. If Abel were to choose which universe to realize, he has no reason to prefer Universe 1 over Universe 2. In both universes, the proposition P (life exist) that is the object of his desire is true. Therefore, if asked to choose a universe, he has no reason to care one way or another.
In order to make Universe 1 more valuable to Abel than Universe 2 we have to give Abel a second desire that Q, where Q is true in Universe 1 and false in Universe 2. For example, we could give Abel a desire that Q where Q = "that I exist so as to experience the fact that life exists." This Abel has a reason to choose Universe 1 and reject Universe 2. However, without such a desire, he has no reason to prefer one universe over another.
If we were to introduce an impartial observer and tell that impartial observer to choose a universe, that impartial observer would have no reason to prefer one universe over another. If we imagine him making a choice, it is because we imagine him having particular desires or preferences, and those desires give him a reason to choose one universe over the other. However, the universe it has reason to choose depends on the desires we assign to it, the strengths of those desires, and whether the propositions that are the objects of those desires are true in Universe 1 or Universe 2 (or both, or neither).
We have a whole host of desires. So, as we look at these two universes, we may well prefer that Universe 1 exists rather than Universe 2. However, this is because the propositions that are the objects of the more and stronger of our desires are true in Universe 1 than in Universe 2. However, this does not imply or even provide evidence for the claim that desire fulfillment has intrinsic value - only that it fulfills the more and stronger of our desires.
There is no such thing as intrinsic value. There is only relationships between states of affairs and desires that give agents with those desire reason to prefer one state of affairs over another.