I'd recommend a UDP (set) over a TB, based on what I've felt from driving Oscar's car (TB, intake, exhaust) and from driving mine (UDP, intake, exhaust).
Aside from the fact his has 17" wheels and mine has 16" wheels, they're mechanically identical as far as the powertrain goes.
Now, I'm in a slightly different position than you will be as I have the SPI with
http://www.escortfocus.com's 50% reduction "race" UDP. AFAIK, no Zetec UDP(s) come close to that amount of reduction - they're all 25% kits I believe.
Still, a 25% UDP setup should free up about 4-6WHP back to the driveline.
It raises the optimum operating RPMs for your accessories somewhat - alternator, power steering and A/C if you have it. Still, it makes the engine feel more "willing" to rev because it is - less parasitic loss due to accessories is a good thing. You also may recover a bit of gas mileage, which never hurts either. :)
A new TB may not make that much of a difference power-wise, but it may help throttle tip-in and overall engine responsiveness. Just don't expect a big increase in power from the wider diameter of the butterfly - chances are you're not going to shovel much more air down the stock intake manifold anyways.
Good luck!