Modding is becoming increasingly more common in games these days. Developers have caught onto the fact that not all players are not brainless kids, but creative minds that enjoy changing their gaming experience using their imagination. I think Minecraft pretty much has a lot to do with it. I'm not saying Minecraft is the first to do it ( Warcraft, Age of Empires, and I think Starcraft had editors to name a few ) but it wasn't so prevalent until recently. The success of a game where you play in a world you create yourself, instead of a static one made for you, finally sparked some light bulbs.
Everywhere you look, mod mod mod. Mod Skyrim, mod Terraria, mod Portal, mod every single thing. Even that new game Voxatron has a building feature where you can design your own levels. It's EVERYWHERE. I remember back in the day playing Pokemon Yellow and always wished I could change the sprite of my character. I didn't want my character to look like this:
I wanted him to look more like this:
But there was no way I could do that. I even went as far as trying to send them a letter in the mail telling them to give players more characters to play as. If they had just given us a way to MOD THE GAME in the first place, my character would have been an awesome undead warrior with a giant cleaver and Death Knight armor. Thanks for ruining the game, and more importantly, my childhood Game Freak.
But back to the point. Incorporating some sort of building or modding feature to your game might not be a bad idea nowadays. The modding community is larger than ever - why not appease them and give them another reason to play your game ( and spend their money ).
TL;DR Version:
LEARN FROM GAMES LIKE MINECRAFT AND SKYRIM THAT ALLOW PEOPLE TO MOD THE GAME AND USE THEIR IMAGINATION TO ENHANCE THEIR GAMING EXPERIENCE BECAUSE NOT BEING ABLE TO BE A DEATH KNIGHT IN POKEMON YELLOW WAS VERY UNPLEASANT.