The question is, what's the ceiling for this team, and also who plays CF for the next two seasons? It does not seem likely that any of our three current CFs are going to be full-time starting CFs going forward (Herrera is the best of them but he'll be another year older and his defense isn't getting better) and the farm options still seem further off than spring training best-case scenarios.
If it is just a wild card team that could end up anywhere from out in the first round to overmatched in the NLCS (two great pitcher and this offense could still produce that optimistic scenario) you probably don't add a starting position player (especially if Segura will return). If you do CF and 3B are your uprgrade spots, barring the big surprise move (but every time we talk about trading Hoskins he goes on a tear. Still think that's the best way to improve the team though, especially if Harper remains out. In that case acquiring a CF would also help, as Vierling and Herrera could still play corner OF too.
The problem is it seems like you'd be buying low but paying high on the current crop of CFs. Still, they probably need an OF, period.