solar panels: we have done this, but there was a time limit for the best government subsidy which has now passed, so it will take you a long time (10 years?) before you get back what you have spent in energy savings. Also only worth it on south facing shade free roof. Doesn't recoup any money when you sell, not seen as a selling point.
worksurfaces: my brother has corian, and says it is amazing, has turnups and splashbacks and doesn't stain at all, any marks just come off with flash, even lily pollen stains. I don't like the plastic look of them, but my mum has beautiful wooden ones, and they mark, and go horrible round the sink and need lots of tlc.
Ikea kitchens have 25 year guarantee apparently. The cost of kitchens is often the cupboard cases, which don't vary much from one make to another, so you can buy cheaper kitchen (like Ikea) and then add the doors you like. Much cheaper than whole kitchen from expensive supplier.
bathroom/kitchen: If you tile, buy an extra box and leave them in the loft/garage. There is nothing more annoying than having to make a minor change in a few years and not having any matching tiles (grits teeth at previous owners who didn't leave even ONE spare tile - and I only need 2 - thus meaning we will have to completely re-tile bathroom, just to move basin and put over the bath shower...)
wooden floor. My mum had sanded boards that were then professionally stained/polished. Looked really fab, didn't scratch, but she was obsessive about wet spills.
downstairs shower is waste of space (who uses a downstairs shower if there is one upstairs) downstairs loo is essential.
wood burning stove: I am desperate for one, and have looked at getting one. We were really surprised at the legal requirements for the space around them. You need a hearth that sticks out 30(?) cms past the end of the door when it is open. This would mean an enormous hearth sticking into our room. I am sure most people don't have this, but suppliers wouldn't fit one that didn't come up to speck. (now trying to persuade dh to build fireplace onto outside of house and knock through..)