Let's just be fair, Ervin and Winker have pretty much been 4th OFs so far in their careers once you factor in baserunning and defense. They make an okay platoon team in LF, but even combined that is just an "eh" result. Assuming either is due for a some breakout is probably foolish at this point. I think Winker will put together a few really good seasons with the bat, if he can stay healthy, but he gives a lot away on the field and if a team is willing to give up a useful CF, 2B or a great reliever he may be worth moving.
I would go hard for one of Ozuna or Castellanos (I prefer the latter) AND make a play at Adam Eaton (moving Senzel back to the infield) as well. If they could land one or two of those three it would really help the offense, pushing one of Ervin/Winker to the 4th man (the other being traded) and VanMeter into a super-sub role.
Senzel's flexibility along with Winker's potential value on the trade marker make room for a number of different ways to go about this. But I do believe the Reds should be using a good portion of their cash on a legitimate OF upgrade.