I have a Waterford track bike (a cheapo CroMo production bike of theirs that they sell for others to rebrand), and it is very similar to the Rush. Considering I have a similar bike, the only advice I can give to you for upgrades would be a decent hubset, with some bullet-proof rims, and a decent crankset, although the set you have seem fine. A saddle upgrade would be considered a fitting requirement, sorta like adjusting the seat height or bar angle.

I have a Phil Wood low flange road hub (same as their lf track hub), laced to a Deep V for the front, and a high flange Phil in the rear. I would definetely rock this but would consider a slighty lower profile rim, or a nice box rim, to save weight and be a little more practical. Definetely go with a 3x front wheel, its much less stiff than radial and more comfortable on the streets.

Other than this, just replace stuff as it wears, like headset/BB, etc. Although with proper maintenance, these things should last a while. It did take me a while to get used the really low rake fork, its heavy and stiff, so it transmits A LOT of harsh vibration to the hands/wrists, but nothing that some padded gloves won't cure. The tight handling makes up for it.