I think he holds good value this year, but I wouldn't look at him as a 2-3 year option as your fantasy QB. He's currently on a strong 5-game run going back to his 3 starts last year. He had a nice start to his SB year in Chicago (2006), but this is his best 5-game stretch of his career. He's averaged about 25 ppg in his last 5 starts, totaling 1,436 yards and 11 TDs (and, yes, more turnovers than you'd like). His previous best 5-game stretch was about 23 ppg (1,243 yards and 10 TDs). And that quickly dropped with the infamous "They are who we thought they were" game and he earned the Good Rex/Bad Rex label.
It could just be coach/player speak, but Grossman will tell you he's never been this comfortable in an offense before. He's said that he went to Houston because he wanted to be in Kyle's offense. According to Rex, there's no comparison between this system and when he was in Chicago. He's much more confident than he was in Chicago.
We haven't really seen Bad Rex for more than a couple drives in a row in Washington. He hasn't had a disastrous game. It could be coming. But, with every additional game that he posts around 300 yards and a couple TDs, he hopefully slowly kills Bad Rex. He has Dallas, St. Louis, and Philly coming up. If he can get through those without falling apart, maybe we can really have confidence in him.
I'm really more of a believer in Kyle's system (assuming adequate talent) than I am in Rex.