Its all league dependent and league format dependent.
I think its worth it for you to do that for 1-2 players, but take a look at matchups/bye weeks when doing so. Waller had his bye, ertz didnt. Ertz has an awesome Playoff schedule So I’d prefer to keep both OR package to upgrade at other positions.
I cant value the players without knowing your league, but see below for relevant info:
I’m in a non-weighted, 14 team PPR 3 player keeper league (we start the draft in round 4) for about 10 years so far and the trends seemed to go like this
Years 1-2 people were hesitant to trade picks.
Years 3-5 people were impressed by high picks. So playoff contenders would rent player. By that I mean trade a 1st or 2nd round pick for i.e. Michael Thomas, then sell him off for the same round pick. (NOTE: Highly suggested you do this before the league realizes it)
Years 6-10 It normalized, and keeper value players would go for multiple round picks (ex: Kamara for a 1st, 2nd, 3rd)
With that all said, in my league trading players for ONLY picks, Fuller would go for like a 3rd/4th, Waller for like a 1st/2nd due to position scarcity, etc…
For reference, the most recent trades this month in my league were Alshon for a 3rd, Sutton for a 2nd Cooks for a 3rd, Ridley for a 4th, Mclaurin for a 3rd.