I've been using it sporadically on this intel machine and it was definitely working on snow leopard…..mysterious.
There used to be something called Rosetta in the older versions of OS X.
This enabled Intel platforms to interpret PowerPC binaries. In technical terms it was a dynamic binary translator.... hence the name Rosetta in reference to that ancient rock some archeologist tripped over whilst playing in his sandpit.
The downside is that the impact on system performance as well as padding up the system with unnecessary code bloat. So after leaving Rosetta for a few years in order to give PowerPC both developers and users the chance to migrate to the Intel architectures, Apple eventually eliminated the Rosetta code entirely in the most modern releases.
So that's why it did and doesn't.
Its removal is a good thing, both developer and user, writing and using natively compiled binaries is always going to be better for both performance and stability.
As for FCP, I'll have a dig around and come back and update....
Update:
I think your chances are limited for upgrade pricing since you haven't bothered to upgrade since 4.x and there have been versions up to 7.x on the legacy branch and now X which was fully rewritten from the ground up. So it's not like you would be looking to upgrade from one or two versions back... you're quite a way back, few vendors would support that sort of upgrade policy.
Your options are to either bite the bullet an go for X or look at Adobe Premiere under the Creative Cloud programme..... I believe you can rent single applications from Adobe without having to rent the whole suite.