Originally, I had been going to answer the question this way:
In your specific sentence, the noun version of the verb spoil is spoiler.
1 a : one that spoils
So, in your sentence, you would use this:
In the beginning, it was a spoiler of the most ecstatic and euphoric experiences...
This simply adds er to the base form of the verb, giving the noun of somebody or something that performs the action described by the verb.
However, that's not what you want. I believe you're confusing the meaning of the verb spoil with what it actually means in this context:
The parents spoiled their child with dessert.
While this does imply that the parents gave their child dessert (but note the use of the verb now, instead of the noun, and with rather than of), it also means that something negative happened—in this case, the child's appetite for dinner was spoiled.
Colloquially, people do say I'm going to spoil you (rotten). But they seldom literally mean that they are going to keep providing something that eventually does end up negatively affecting the person (making them rotten). When somebody say I'm going to spoil you with gifts, what they really mean is, I'm going to give you an excessive number of gifts.
Since I'm going to spoil you (rotten) and I'm going to spoil you (with something) are idioms, you can't really use the single word spoil from those expressions in your own sentence and have it mean the same thing.
In theory, you could say:
In the beginning, it served as such a distraction that it spoiled their financial health with the most ecstatic and euphoric experiences, preventing them from even thinking about going to work.
But note how that changes the meaning of what I think you want to express.
Based on the description given at the end of your question, what I believe you're actually looking for is the noun form of a verb that means the opposite of spoil:
In the beginning, it was an enabler of the most ecstatic and euphoric experiences...
Now we have a noun form, and the sentence only has a positive sense (discounting the initial in the beginning, which implies that it stopped at some point).