FWIW most players are inconsistent at least when it comes to scoring. Look at Nash for the major portion of this season. Callahan has been playing with Richards and Hagelin--they've all have been inconsistent as far as putting up points.
The thing is whatever other ways a player can help his team when he's not scoring. Nash really doesn't do a whole hell of a lot either when his game is off. Callahan has a lot of ways of helping his team--penalty killing, forechecking, just being a guy who plays with grit all the time and even when not scoring you get a consistent effort.
As far as Stewart is concerned--he would immediately become the Rangers toughest player. He is big and he can play mean. Though not a really frequent fighter he has an impressive fight card--Westgarth, Jared Boll twice, Colton Orr, Prust, Gazdic, Clifford, Bollig, Roussel, Zack Kassian twice, Carkner, Souray and Prout amongst others. He wins more than he loses. He's also a guy who is capable of scoring at a decent clip. A one time 60 + scorer. Add him to a 2nd round pick for Callahan who is going to leave the team unless he decides to take a lot less--it's not really a bad deal IMO. Stewart helps address an issue the Rangers have had in the past in the playoffs being outmuscled too often by bigger, less talented teams.
The thing would be to get Stewart to give his best effort consistently. He's not frigging Wolski though. A completely different animal IMO.
We come away with a 2nd anyway and we can move Stewart later on if he isn't working out.