Ummmm...ninja or not, I think Motorex is the only game in town.
Why do you think Motorex is a rip off?
Another thing to keep in mind is that it's probably going to be expensive and difficult to insure a grey market vehicle depending on the state where you live.
I'd keep the Evo and it's warranty, but that's just me. For the cost to import a JDM vehicle, you can buy a hell of a lot more car here in the US, IMO.
Edit: Keep the Evo, take the money for the Silvia and instead use it to buy an Sti to keep the Evo company.
The more I think about this, I'd say it falls in to the category of "if you have to ask, you can't afford it". If you had enough money and contacts, you could most likely get any car you wanted in to the country. Legality is another matter.