Home brew cars yes, replica's mmmmmm nah.
Also make sure you do your homework before stumping up the readies.
http://scamsonline.wordpress.com/2008/08/05/supereplicas/
However if you build one of these, I have dibs on shotgun. 
http://www.ultimasports.co.uk/Content.aspx?f=gtrintro
Looked into building one of these myself tbh 
Yeah I noticed there's loads of scams, especially in the states an the one you pointed out in particular, even the utube videos use other companies hard work.
nom nom at the GTR, well I've got confirmation the audi 4.2 fits, shame it doesn't have many ponies as I like but 340ish bhp should be enough, the noise will make up for it. I wasn't a huge fan of replica's a while back, but I've slowly started to like them over the locusts everyone one seems to build, plus its a head turner, even if its not a real deal. Its like my mk4, when I got it no one had it, then everyone had it, mate got a cupra mk2, no one had it, now everyone and the undercover police have it. With certain kit cars people think they are classics or go "WTF is that", with a replica super car or similar they get excited... but people have different tastes and opinions, I've slowly started to appreciate replica's and fancy a go, sadly it comes with a huge price tag which means I need to be 100% sure I want to go ahead with it before making the decision and not regret it.