noms are not 'weighted' in the way you describe. A nom is a nom, regardless of where it comes from and neither has more or less weight than another.
However, different types of nominations have different numbers of available slots available. For instance, all Congressional nominations have 10 noms for each available offer of appointment (slot) or 10:1. Service connected noms are different, ie. there are usually 800 or more Presidential nominations granted, competing for 100 slots, or 8:1. For NROTC, there are usually close to 300 nominations competing for 20 slots, or around 15:1, etc etc.
In the national pool (where applicants go if they don't win their nominating slate), the first 150 slots are given, by law, to the top 150 ranked by WPM (whole person multiple), and they must have a MOC nomination.
So, in terms of the national pool, yes, MOC nominations are weighted more (because others are not eligible for the top 150), but there is no difference between a Congressman's nom and a Senator's nom. It may be that the competition within the slate is higher (because candidates are competing statewide) but the SA doesn't give more weight to one over the other.