Can my builder's grade cabinets be stained darker?

Lightly sand,clean ,prime with Zinser or Kilz,and paint. Same process to stain,however my opinion I would with stain or paint to keep it uniform.Another thought they are not ugly as you say by far. If you just updated to hardware it may just be the change that is needed.Fyi Just a thought.

I've had good luck using gel stain (Minwax). Lightly (and I mean lightly) sand the laminate panels, then apply a gel stain in the color that you want. Dry and lightly sand again, apply another layer, and continue to do this for about 3-4 layers. Then after thoroughly dry apply a couple of coat of polyacrylic with a light sanding between the coats of poly. I did this to a laminate dining room table top. It has had heavy use for a couple of years now with no problems. A lot of work but worth it. Painting a dark color might be easier as in the answer above.

You should be able to tell if there is laminate involved with the sandpaper. If there is (which it does not look like) you could paint all the cabinets.

I invented my own stain/paint combination that so far is working well... I wanted dark expresso cabinets. I combined Rustoleum Leather Brown paint with equal parts of black oil stain. I sanded lightly, painted my combo on, then protected with polyurethane that I wiped on with a soft cloth. That was three years ago and so far, so good. I was afraid of chipping and wear at where the doors are opened, but this has worked.

I agree with Janet, they are beautiful!!! Just change out the hardware to give an updated look.

black appliances as well. Cork flooring.