yeah it's hard to say what will generate, I've created around 30 dimensions in a row and all void with nothing -then the next day 1st one and got large orbs (finally) which I then used a feature absorber in so I could create a dimension with orbs of diamond, iron & gold.
I think all dimension created have some small bone structures around floor level and dimlet buildings throughout, unless you use dimlet to specify not to create these.
To delete a dimension from the dialer, I use the safedel command - full list
here
/rftdim safedel <dimension>
- with dimension being the ID shown in the dialer.
edit: one thing to do to help get different random dimension when looking for certain features is to add digit dimlets, you can then just extract your dimlets and change the digit.
Digit dimlets: use digit dimlets to make new unique worlds using exactly the same dimlets as another world you just created.