To be honest, vanilla hacks will bring nostalgia for those who are playing, for example: this hack
definitely felt like a perfect sequel to SMW when I played, none of the level design is really surprising, but it still felt like a great adventure made by nintendo themselves.
But it is possible to do more than that in vanilla hacks, think about the 1st super mario maker game on the WIIU it was pretty limited but still people had find lots and lots of ways to surprise using the same elements.
I think the same can be done with the original SMW assets, its not about the number of assets you use or limit yourself, but about HOW you use them.
The original vanilla game used his objects the way we already experienced, but in what other ways can these same objects be used?
Think about how every object in the vanilla game interact with each other and all the combinations that are possible, if you can keep thinking of new ways and level ideas not seen before, it can definetely surprise the player.
These two hacks
for example had me for a spinning when I saw some of the level ideas in them.
But still, even if you want to keep the vanilla feeling of the original SMW there's nothing wrong with using new custom elements or custom paletes and music once in a while.
After all the visuals of the original SMW can get repetitive pretty quickly and you may run out of ideas eventually.