On my way home from work I thought about it some more and somewhat changed my mind... I would keep the Proficiency base bonus the same (+2 to +6) and then Skill Focus would have the same affect as Expertise (proficiency bonus twice). Then base Defenses would be 1/3 character levels (round up) plus their best Class bonus and Attribute modifiers.
Now you have to re-work the TN for most skills. In Saga most are in increments of 5 but I would go 2 then 3, then 2 starting at 8 (so TN would go 8, 10, 13, 15, 18, 20, 23 and 25).
I was thinking about allowing some of the low-powered Force Powers to lasting longer but might have to just go through all of them one by one