I do not see how either of these could be a waste of money.

I can't imagine anyone ever regretting having a slab poured.

There are a few people on here that always say put the money into the things you can't see inside the walls, etc.. I would put the foundation in that category and forego any of the extra interior options.

Neither runners nor a slab are any guarantee that the house will not settle enough to need re-leveling. That is simply a matter of how much the ground will settle. I will say that a slab is nice when any work needs to be done underneath the home. It lets you (or the workman) use a mechanic's creeper to work and not be laying in the dirt.