The issue is that the companies who sell/install this stuff will tell you anything to help get the sale. We had one of the wardrobe places and the guy was utterly convinced that each penny spent would also directly increase the house value by the same amount.
Unless it is an extension, it is unlikely to have a huge impact on the value of the house. Even things like kitchens/en suites, as the new buyer likely has different taste. What they can do is make the house more desirable which could end up in a bidding war between potential buyers, but there's no guarantee.
We've considered a 3x8 single story extension on our house, but ultimately I don't think we'll get that much back from it come sale time, as the house is pretty much at the price ceiling for the area we're in as it is.