I'm a newbie to the fixed gear world. I usually ride a Specialized S-works CX but recently saw a great deal on a Soma Rush in my size on Craigslist. It was a custom build, practically new, and I was able to pick it up for $400. It's a lot of fun and I'm enjoying riding fixed for a change.

The bike is great overall, but I am getting the "upgrade itch" and wondering what the most cost effective upgrades might be to reduce weight (the bike weighs about 19.5 lbs currently), or improve the ride.

I've thought about adding a carbon fork to reduce weight and improve ride quality, and am considering the Wound Up carbon fork as it seems be one of the only 1" carbon forks with a rake similar to the stock Soma steel fork. This would shave about a pound off the bike, but I'm not sure if carbon would make that big a difference over steel in terms of ride quality.

Are there any upgrades more experienced riders here might recommend? Here's what I have right now:

Soma Rush frame and fork, 58cm
Aheadset C4 headset
Origin 8 pro-fit alloy stem
Nitto alloy risers
Oury grips
Shimano tiagra front brake
Sugino TL crankset, 170mm
SSK Chain
Surly rear cog
Novatec track hubs
Mavic Open Sport rims
Maxxis Re-fuse tires 25cm
MKS track pedals
Alloy seat post (not sure what brand)
Specialized sonoma gel 155 seat

I know it's a slippery slope, but I'm curious what others might upgrade first, if at all. FYI, I'm using the bike for NYC streets and blasts around the park. It's more of a second "fun" bike (The CX is my commuter), so I don't usually ride more than 15-20 miles at a time on it.