It's lucky for everyone that a crystal can cost as little as 25p. As long as the exorcising and purifying is within your budget then go for it. It can't hurt. Personally, though, it would hurt me if the stuff cost more than I could afford and then didn't live up to my expectations.
A clean tidy home smelling of vanilla, furniture re-arranged to give more light and space, flowers, hand painted pictures on the walls, new paint, new curtains, drapes or cushions if money allows - all this sounds good to me.
I have also found that clean windows make a huge difference inside a house, also a tidy garden - improves the view from your windows. And window boxes you can see from indoors too.
Could you consider moving the TV, stereo or computer to other rooms? this would instantly alter the feel of your house as different activities would happen in new places. Glass picture frames are cheap to buy if you look around. Can you collect some of your favourite photos and make a collage of them? And make a new display of your children's artwork. Buy some cheap storage boxes (ikea?) and de clutter. Make one room if possible into a well organised spare room - put boxes in here plus anything you don't like the look of, but need to get to easily on occasion. An extra burden, true, but how about buying a cat? probably too much to take on now, but a new loving presence in your home could lift your mood and a lot and help change the feel of your home.