I found a Puffadore essence today, but I dunno whether to sell it, or not... :/

I like Puffadores, but I could also use the gold...

I always think "gold is forever, certain items are not."

However, it depends on how easily you make gold. I think if you play this game well enough, gold is easy to make (ie I do missions).
If it isn't, it makes sense to sell items.

For essences, I tell myself "will I make a pet now or later, and will I USE it?"
Use = breed/battle/missions
If none of the above, I save it, or sell it. Personally, I save them (since new genes/mutations might come out that make using them appealing).

Those are my 2 cents. :)

Hm...

Well I guess it'd make sense to save it then based on your answer.
I don't make a lot of money, but I doubt I'll come across another essence like this in a long time.
And since my sister has a female one I got for her before I could make a male one and match it with hers. :p

Thanks! ^.^