Investment(Brood Vanity)

So I'm new to this game and also new to this long-term investment thing. I know prices rise and fall because of supply and demand, but I was wondering if brood dragon vanity from event is a good long-term investment? Did vanity from last year's winter event rise? If not vanity, what's a good investment that could possibly give good returns? Locks? Pets?
Ty :)

Mostly locks and pets will go up since they will run out after a time.

When to buy locks(lowest price) and when to sell locks(highest price)?
Also, we are talking about Ren'Gols or the event Brood locks?
Ty :)