That nylon bushing does it's job... in their stock form they are a bike nearly anyone can ride with complete confidence.
I have upgraded a number of 20's with proper headsets and the steering is much quicker and takes a little getting used to, especially when you are also running drop bars and ride in a more aggressive position... but the 20 will forgive you for things other bikes won't and is very recoverable when you push it beyond it's limits.
Custom frames and forks tend to run upward of $1000.00 while a mass produced version would be significantly cheaper but I will ask how much it would cost to replicate the Twenty with better quality tubes and standardized parts.