My ATF55 was sold to me by a dealer at the exact time the new TS55 replaced my model. When asked about the differences between the old and the new, he termed them as "largely cosmetic"
Now that I've used the ATF55 for about 30 months, I think the changes are a bit more than simply cosmetic: the power cord, the dust port, the composite baseplate instead of a stamped steel one, the easy blade and riving knife removal. Of these I think the only meaningful one would be the the splinter gaurd. But even that depends on the kind of wood you'll be cutting. For me it doesn't matter, and a new dealer from whom I've now bought 4 additional "green machines" advised me not to switch.
Gary, here's a weird twist, though. People don't mention this minor change, but the indicating scale for bevel angles is really, really easier to read on the TS55. Us old guys with bad eyes don't need woodworking bells and whistles as much as we need help seeing.
Gary Curtis