AE is a tool that goes alongside your non-linear editing system. you shouldn't replace vegas with it, but you might want to consider doing your effects in it and then bringing them into vegas to edit on a timeline.
Should upgrade to premiere, then you can link After Effects files seamlessly.
The best way to do ramp slomo is shoot at 60FPS with a higher shutter, ramp no lower then %40 ( 24fps ) at lowest point. drop that in a 24fps timeline in premire.
after effects is the only way to get correct ramped audio(without audio post prod) to my knowledge.