I just purchased last summer in Park Terrace, mission bay. I didn't have the hardwood floors put in but I will be doing so before I sell. My carpet is getting wear and tear now but I will be upgrading to hardwood for sure before I sell. I recently had my place reappraised and the appraised value was up significantly over the past 6 months.
My advice is: don't do it just for the investment aspect at this point. If you WANT the upgrade, go ahead now.
The benefit is a mixture between your personal enjoyment and investment. If your unit is highly luxurious, there is a deep market for such units in San Francisco. It's the starter properties and lower priced ones that are being hit by the subprime crisis.
Other than simply wanting the upgrade, it depends on how long you've been in the unit, when you plan to sell and what the market is like. If you would like me to send you market information, let me know the address and unit, I will send you a market analysis. Bwilliams@ubayp.com or give me a call and I'd be happy to discuss it with you.
Please ask your realtor first as he/she knows which unit you purchased. Updating at this point in time is for your use and enjoyment as noted by Jed. The updates today will be older and show wear and tear by the time you sell. Most people prefer all hardwood today as it is easier to keep clean - in five years, who knows?
The areas that appeal to most buyers are Kitchen, baths, then overall appearance. I can email some specifics if you like. The bottom line is, I would upgrade, now, so you can enjoy it while you like there. The payoffs are a bonus when you sell.
This may help you.
Go to realtor.org and type in home improvement