wow, thats extremely long term issues and i'm surprised you've persevered for so long and at so much expense...most would have chopped the car in so well done for sticking with i as long as you have.

i've got a mk1 focus (2000 w reg) and i had a vibration issue for months. didnt go away when i changed the hubs and calipers (upgrade to st170 front brakes) and it got worse when accelerating and braking but lessened at constant speed (not costing). every time i jacked the car up i couldnt find anything wrong but weirdly it would disapear for the first 5 mins and then come back. even got BRAND new wheels and quality Brand new hankook s1 tyres as my wheels looked crap and still didnt cure it. eventually worked out it was the inner tripod joint on the drive shaft. changed for a perfect set of used shafts for £65 for the pair and fixed it. new are rediculously expensive!!

now i'd suggest you change yours BUT your problem got fixed and then returned with a warped disc which to me rules out the shafts!! this means the problem must lie at the hub end or possibly a lose steering rack.

i'd take it back to ford as they havnt fixed the fault and get them to specifically check the rack is tightly bolted down and then the checks tabetha (whos more knowledgable than i) suggested starting with
- checking the hub flange is true
- take calliper off, fully clean up the pad carrier sliders, strip the slider bolts out and give them a clean up and fresh grease and then refit it all and test (providing the current discs and pads are all true.
- then further checks tabetha suggested.

hope this helps.