Heads Up: Visitors in Dragonvale Don't Do Anything
What is Dragonvale? Think SimCity meets DinoPark Tycoon. You hatch and breed dragons, and each has its own habitat requirements and earning potential, which can be impacted by level and boosts.
You know what DOESN'T impact earning potential? Or anything else?
Getting More Visitors
What do Visitors do in Dragonvale? They make your park look busy. To the best of my knowledge and internet sleuthing, visitors do not impact how much money you make in Dragonvale. Dragons continue to earn the same amount per minute whether you have people packed into you park like sardines, or it's a ghost town visited only by tumbleweeds.
They may as well be decorations. Which brings us to...
What about Decorations?
With the exception of some achievements related to purchasing and placing certain decorations, and the boosts you can place that actually increase certain dragon's earnings per minute, these digital decor items are for the purpose of attracting more visitors - which, as we stated above, doesn't really seem to impact your bankroll in a meaningful way.
(Granted, I still did some light decorating on my first island because I needed to create symmetrical pathways for the good of my soul.)
If you're playing to win like an investor, skip the lampposts and pour your dragoncash into things with meaningful returns, like dragons, habitats and food.