A couple of years ago a near neighbour of mine spent £30,000 on a loft conversion. He also had his garden landscaped with an extensive bit of decking and shortly after that he put the house on the market just as prices plummeted. To my surprise, and his I think, he got the full asking price. He also managed to buy a much larger house for not a lot more money. All this while others looked nervously waiting for the market to bottom out.
The new people moved in and had a new kitchen fitted and a few weeks after that the deck was on the skip and they were having Indian Sandstone laid. They are still having work done and a good many local tradesmen are grateful for it.
There is of course no guarantee that the current owners will see a return on their outlay but hopefully they will enjoy living in the house. In the end that it what home improvements should be about. If you enjoy living in a house then there is a good chance that somebody else will also enjoy living in it and to my mind if you focus upon that the investment is secondary. It might seem like an obvious statement but 'houses are for living in' and when we lost sight of that simple truth and started treating them as banks we became the architects of our own downfall.