People justify expensive home improvements by saying that they'll "pay for themselves".  That means they'll add more to the home's value than the cost of doing them.

But it turns out they usually don't.  According to Yahoo Finance the only renovation that increases the cost of the home enough to recoup 100% of the cost is replacing older doors with steel ones.

Replacing the siding recoups an average of 80% of the cost.  New windows get back about 70% of the cost.

One of the least cost-effective moves is to remodel your kitchen.  It only gets back about 60% of the cost.  Mainly because it's wicked expensive to do:  They cost an average of $113,000.

The other problem with a new kitchen is that it can't be seen from the outside.  Shiny new doors and siding make an immediate impact to people passing through the neighborhood.  You have to already be interested in the house to ever see the new kitchen.

For the same reason, turning the master bedroom into a suite, adding a deck on the back of the house, and renovating the bathrooms also only recoup about 60%.

But even though they don't pay for themselves, you might still want to make improvements.  Often, a major improvement makes the difference between selling a house or having it linger on the market for months.