If you put a lot of work into your home, then it is worth every penny. You live in it an need to be happy and comfortable residing there. As such it would not be for naught.
I think the answer to your question depends on who you speak to you, the location of your property, and the price range. It also depends on what you mean by slide -- prices are always adjusting based on what people can or are willing to pay. Keep in mind that many economists currently assert that once prices bottom out, then prices will stay about the same for a few years as bad loans work through the financial system. In which case, the real price for your home will actually decrease relative to inflation during that time.
If you look at the price per square foot, prices appear to have stabilized for now. There still is some uncertainty in the market and it appears that a large percentage of the homes currently for sale are distressed and being sold in a short sale or at some other point in the foreclosure process. Judging by the number of homes that have been on the market for 180+ days it seems the market may drop further or at least to bring those homes in line with averages for comparable homes that have sold. Moreover, relative to the average price per square foot, the market will discount homes next to undesirable hazards such as the trains running down Mission or the freeway. Also, some higher priced homes seem to have have prices disproportionate with the area so I expect will see declines as well. The Calculated Risk Blog is a good resource in understanding some of the macroeconomic forces at play.