Very pretty bike. Just look on eBay to see values, search for completed auctions. Your rear quick release skewer is missing (bike is unrideable without it). The bike could use bar end plugs and nicer bar tape.
You can get a "modern" bike that will be lighter, but if you are just riding around NYC you don't need a super lightweight bike (no long climbs), to get "a lot" lighter in a new bike will cost a lot ($4K+), and it won't get near the looks and appreciation (by knowing riders).
Basically, if you only ride 600 miles in 4 years, there's really not much point to replacing this bike. As wall art, it is hard to get a carbon bike better than the 200Sci. If a bicycle were to be in the MOMA, the Kestrel 200 would be it.