The Vikings traded the Dolphins pick 86 in the 2016 draft which according to
this chart is worth 160 points using the JJ method and 6.2 using Chases method.
In return they get the Dolphins 3rd round pick in 2017 a conditional 4th round pick (could be after the 4th round comp pick) in 2017 and pick 186.
Pick 186 is worth 17 points on the JJ or 1.3 on CC.
The picks next year we do not know where they fall. However the 3rd round pick has pretty good odds of being higher than 23 unless you think Miami is about to make a deep playoff run.
Pick 80 would be the middle of the 3rd round. This is worth 190 points JJ or 6.7 CC. The end of the 4th round would be pick 128. There were about 9 comp picks after round 4 this year, however Miami might not be getting a comp pick and their 4th rounder would then be likely higher than 128 so the value of 128 seems like a medium of these 2 possible outcomes. The value of pick 128 is 44 points JJ or 3.7.
The totals for this deal are
Vikings 251 points JJ or 16.6 CC compared to 160 points and 6.2
So the Vikings are winning this deal by 91 points or 10.4
Now we want to time discount the 2017 picks because picks today are worth more than picks next year. You suggest doing this by discounting the 3rd and 4th round picks by a round.
Pick 80+32 = pick 112 = 70 or 4.6
Pick 128+32 = pick 150 31.4 or 2.7
So the Vikings would give 160 or 6.2
for
118 or 8.6
This would be losing 42 points on the JJ but gaining 2.4 on the CC.
The other thing to consider, and basically what Rick Spielman said was they didn't think the players at pick 86 were significantly better than players they can get later on. If there were a player they valued high enough, he did say they had two picks in mind for 86 but that they can get similar players later on.
There are several indications from the draft so far that this is a WEAK draft class. So why not move a pick after the top talent is gone for talent in 2017 that has a good chance to be better than this?