Wow, some of these trades are really selling Alexander low. Seriously, SA is a good BUY right now. Look at his upcoming schedule: home against NO and STL, a bye week to rest up, then at CLE and home against SF. Those are 4 games in a row of favorable matchups, three of which are at home.
Besides, despite his declining skills, he is getting the carries, and is the man at the goal line. A bad (OK, horrendous) game at Pittsburgh aside, he has been pretty solid:
Week 1 TB : 105 rush, 1 TD; 2 for 12 rec ~17 pts
Week 2 @ARI : 70 rush, 1 TD; 2 for 5 rec ~13 pts
Week 3 CIN : 100 rush; 2 for 8 rec ~10 pts
Week 4 @ SF : 78 rush, 1 for 5 rec ~ 7 pts
Week 5 @ PIT : 25 rush, 3 for 7 rec ~ 2 pts
There is a definite downward trend in this sampling, but the first three games were all solid RB1-caliber games. The last two were on the road, one against a division rival (always a tough matchup), the other against a top 5 rush defense. So I think the decline in production has less to do with Alexander and more to do with the opponents he faced. As an SA owner, I ride him at least until the bye week (depending on how well he does), and try to sell him then. If I don't own SA, I try to buy NOW, after his worst performance of the year, and start him with confidence for the next two weeks at a minimum. All this assuming redraft.