None of these are dumb questions – to answer:
-The Stereo Room Vintage algorithm in SP2016 Reverb is close to the 2016 Stereo Room plugin, but it is not exact. The SP2016 Reverb version more faithfully emulates the filters in the converters, bit rate, and sample rate of the original SP2016 box. But, the two will sound close. SP2016 Reverb also has 5 additional reverb algorithms to chose from.
-The presets from 2016 Stereo Room are included in SP2016 Reverb, but there's also a whole slew of new presets.
-Crossgrade means you get to keep your current 2016 Stereo Room license, but get the SP2016 at a larger discount than the standard $79 sale price.
-The difference in CPU level should be close to negligible.
Hope that helps!