I actually think the Niners should trade down from both number one picks.
This draft is very deep at a number of positions. The Niners could actually find a number one WR in the
second round this year. There are 16 WRs rated "A+" or "A" according to Draft Scout. Getting one of the top 3 would be nice but when one considers the recent track record of WRs drafted in the first round and the other needs the team has (L OT, OG, CB, DT, Edge rusher, and backup TE just to name a few), taking a wide-out in the first round is a luxury the team cannot afford.
With that 13th pick, the Niners could conceivably get 3-4 picks in the top 4 rounds out of it,, fill a number of needs with those choices, and then the Buck trade starts to look pretty good. If they trade out of both picks, you are talking 5-6 picks in the first 4 rounds...and again, this is a deep draft. If the team plays its cards right, they could really stock up.
Cheers!