To address the second point first, Kyle Korver isn't available anymore, is he? Rudy is one of the top names on the market right now, and while he is not an elite shooter, he is a good shooter and has a lot more in his offensive arsenal than Korver. We should expect a similar return.
To the first point, sometimes you get nothing. Sometimes, in fact a lot of times, that's the way it works. Right now we are also looking at losing players like Darren Collison and Ty Lawson and Omri Casspi (who is not even playing) but nobody seems to be suggesting that we send those guys off for a second-round pick and nothing. The reason that the general consensus here is that we should trade Rudy is that the general feeling is that we will get good value in return - something that will actually help us down the road. For instance, reports that we had the framework of a deal for Payne in place before he was hurt tell us that teams are in fact willing to give something good for an expiring Rudy. But at the same time, we have to hold out for a reasonable deal. There must be a value line below which we will not go, and while I'm not certain exactly where that line is, a second-round pick and nothing is easily far below that value line. If teams decline to make a value offer and we buckle at the deadline and panic-trade Rudy for a second-round pick and nothing, no opposing GM will ever take Vlade seriously in the trade game again. They will know that all you have to do is wait the Kings out and the Kings will buckle. And our reward for giving the league ammunition against us in every future trade is a second-round pick? That's not worth it. Any return below the value line, we must say no. And we say no not because a tiny return is not better than no return, but because ensuring that we are not walked all over in all future negotiations is better than a tiny return.
Yes Korver isn't available anymore, but still Rudy's skillset isn't really what the upper echolon teams are looking for. Rudy is at 33% from 3 this season, which makes him a below average shooter from 3. Of course Rudy is one of the best overall packages available at SF right now, but he is a pure scorer and a guy, who wants the ball in his hands and who wants the ball in the mid range and paint area.
Now every team currently in the playoffs ranks has either a great starting PG (Cavs, Raptors, Celtics, Hawks, Pacers, Hornets, Wizards, Warriors, Rockets, Clippers, Grizzlies, Thunder, Blazers) or a SF able to create offense for his teammates (Pacers, Spurs, Jazz). There is no need in the starting lineup for Rudy, because they want the space in the mid range and paint area open for their guards to penetrate and kickout. You could make a case for Rudy as a bench scorer, but this means the offensive schemes would change entirely for the team from pick&rolls and kickouts to mid range ISO and post ups. We also have to keep him mind, that teams tend to play their stars more minutes in the postseason, which means less time for Rudy to play his brand of basketball. He simply isn't a great fit for most starting lineups in the league and most teams will most likely be hesitant to trade for him strictly as the offensive ISO spark plug off the bench, because this will make their offensive schemes somewhat obsolete and we have to keep in mind, that Rudy will still demand a lot of money next offseason.
I think Rudy is in a very similar spot like Greg Monroe right now - an extremely talented player, but because his game is a bit outdated and because he is not a lockdown defender most teams will be hesitant to give up valuable assets for him. This atleast is as long as he views himself mainly as a SF. I can envision Rudy on some teams as a small ball PF, but he has to play tougher and defend more willingly to be good in that role.
To go into the season with that many expiring contracts was a mistake from the beginning. We are one of the least talented teams in the league right now and only half way decent, because DMC is keeping us afloat. Wether it's DC or Rudy or Casspi - letting talent walk for nothing is not a good thing to do and will hurt Vlade's reputation far more, than making low value deals (I agree, that a mere second round pick is out of the discussion but I woulnd't rule out a struggling young talent or something similar. We can't think only about this season, but must keep 2017/18 in mind). Vlade has brought this onto himself. He wanted a team with a lot of short term deals. The risk of this kind of strategy was always obvious.