Last year, PJax mentioned that he thought Free Agency should come before the draft so teams could better identify needs to fill through the draft. Clearly a window into mindset as he sees FA as the way to fill the starting lineup rather than drafting.
I mention the above because of the timing aspect. By trading a future pick for a SG before FA, you really don't know what kind of team you will be left with. Every year you identify undervalued players. That said, any additional picks we acquire will absorb valuable cap space as this team tries to complete its starting lineup (let alone fill out the bench). Thing is, second round picks don't really use up cap space as they are the same value as cap holds.
Two things result from this: 1) Unless we knew this player Valentine was the player that puts us over the top, you really can't make this trade before free agency. If I knew I was signing KD, I might make that trade all day. 2) The talent identified needs to be draft able between 31 and 60 to be cost neutral before free agency.
A third, less important point, is that 2017 draft picks are economically more valuable than 2016 based on the rising salary cap. Rookie scale contracts are fixed price by the CBA. It just means that the percentage of total salary that a rookie scale contract takes up in 2017 will be less than in 2016.
There are good counterpoints to these statements. For example, picks 31 through 60 are not fixed price for 5 years... So they cost more in the long run if you have a good pick. I don't think you use this logic though. It's like a winning lotto ticket. If you have a winning lotto ticket, do you complain about the taxes?
Long story short, you should not trade the 2017 pick for 2016 because of the timing of free agency. Valentine would have to be a 90% or higher odds to be above average this first year to make me change my mind. I don't think the odds are that high. Anything less, I'd rather let you pick next year's Valentine next year.