After playing HayDay a bit more, the gnome concept is coalescing for me. Not only would it be unique, it would provide completely different game dynamics. It would not just be a Farmville / CityVille / HayDay type of simulation game in a different fantasy setting, but something more.
I wrote a lot about what worked for me in HayDay. The goals and possible actions are always clear to me, and nearly every action works towards the same goal - building out my farm. I’m always clear on what I should or could be doing, and it seems that nearly every possible interaction with the game is tailored to improve my farm (buying items from the stands, harvesting, doing the little quests, etc.).
I’m interested to see how you’ll incorporate the gnome system into the game, and want to hear more around them. How are you planing to incorporate them into the game’s design - are they a central component, the core of the game? Are they something players can do to pass the time while they wait for their crops (or whatever) to grow?
It sounds like these gnomes are what sets your game apart - so having everything feed into the concept of using gnomes would reenforce that concept.
Keep in mind I only have a cursory overview of what you have in mind for your game. It sounds like the gnomes are a key part of the gameplay, so making it prominent early on at the expense of some of the other dynamics (harvesting, buying buildings, etc.) might make sense.
The gnomes should be given as much prominence as the importance you’re placing on the idea. I think there's a TON of potential to really stand out by making the gnome idea the sort of core gameplay experience. It could be described in the title, in the game's marketing, etc. However, if it’s a side feature and not absolutely critical to the gameplay, it might be ok to hold off on introducing the gnomes immediately.
The first gameplay experience is like reading the first page of a book. The first experience is a sort of promise of what’s to come; a summary of the entire experience. The core experience of the game should be felt immediately. It should be obvious when you see it, and it should coalesce when you play it.
As much as we don't admit it, we do judge books by their covers. I'm more likely to pick up a book that has an interesting title and cover than I am for one with a bland and unexciting visage. Everything the game presents to you should reenforce the main experience - the main feeling of the game. If the game is about gnomes and setting up paths, and the game's title and cover image reflect that, people will understand what they're downloading and you can have an easier time gaining traction and retaining users.
The gnomes can provide a deeper level of engagement around customizing your town than what HayDay and others provide. The way you arrange buildings in HayDay might make things easier for you, but there’s not really any rules around it, so there’s no reward around having a nicely structured farm.
Creating the paths / markers for the gnomes could be an actual game component in that you can create optimal paths. By playing around with the paths, you learn which paths are best to create the most efficient routes, and you could imagine having to change and optimize paths as unlock more buildings. You have the ability to be creative in your path creation, and you can also be rewarded for being creative.
The freeform nature of building placement in HayDay does provide two important things (that your gnomes can also provide): Customization and Exploitation.
Being able to creatively customize how your buildings are placed is important, and you can still have that with the gnome pathing. Exploitation is not a bad thing - it’s a way to cleverly get around some constraint; not cheating, because you're still within the confines of the game's rules. Essentially, it’s what your dad did when he left stuff outside his buildings to get around the barn storage requirement (he got around have to pay for a resource: storage space).
These kinds of tricks and exploits are important to have (as long as they don’t create completely unfair advantages). You can get around the storage requirement...but you still have to harvest, you still have to use the resources. The gnome system could allow for even more exploits and creative tricks.
It seems that there could be a ton of different mechanics around the gnomes, which could, if you wanted it to, make it play a lot differently (but similar in some ways) to HayDay. The game sounds like it could more about managing the gnomes than managing the farm ( recharging batteries, creating paths, upgrading, customizing, etc).
Creating the paths / markers allows creating a customized towns, which allows you to not just express your creativity (like in Hay Day), but is actually a game component in that you can create optimal paths - you can learn which paths are best, create the most efficient routes. As long as inefficient routes aren't really penalized, more efficient routes could give you bonus rewards.