If your home was built in 2002 then it should be pretty much updated with newer systems throughout. To maintain the value, just make sure you maintain the home. It might be time to repaint some rooms, depending on the wear and tear....or even the exterior. Make sure the landscaping is also maintained, and that you have replaced any plantings you may have lost over the years.
As far as increasing the value - if your home is missing any amenities that are common in other homes in your neighborhood (2nd car garages, finished basements, decks or patios)...then those mght be good to consider IF, and I say IF, you want those amenities!
Otherwise, just enjoy living in your home!
As far as how long you should stay in your home - no one can answer that for you. Call in a local agent and find out what the value is now..........if the numbers work for you, then you can make that decision. I would assume that having bought in 2002, you should be in a position to make a profit. Whether that profit is enough to allow you to move and upgrade, only you can determine! The best time to sell is when you're ready and in a position to move on.
best wishes in the future.....
Prudential NJ Properties