The best idea is to pick him up now in keeper leagues. He's going to end up the closer in Oakland later this year possibly, and without question next year. Dotel is a FA at the end of the season, so Beane might well try to move him. If not, he certainly won't be resigned.
I don't buy into the idea some people have thrown around of him taking over Dotel's job... that would lower Dotel's value too much on the trade block.
I have Street on my 10 team keeper as this years lite version of K Rod of last season. He will make up with K's that I lose with a pitcher like Hampton who doesn't get me any. He was a complete homer pick as I love the Longhorns but he has an outside chance of getting the closer spot sometime this year either with an injury or trade. With the guys in my league, I'm never fast enough on the draw to pick up players that immediately become hot commodities, so I went ahead and drafted him. It could be a bad long term pick for this season but I took the chance and it appears to be a safe harmless move for my RP spots.
"Relievers are like volatile stocks. They're the one asset you need to watch closely, and trade for quick profits." --Billy Beane