I am in no way a fan of Steve Sidwell, but I'm not sure if Sidwell leaving is automatically a positive. If Villa plan to stay competitive both domestically and in Europe they are going to need to use some of their depth, and said depth takes a bit of a hit of Sidwell is shipped out. The news on Fabian Delph's recovery is positive as of yet, but he should not be counted on to any degree in 2010/2011. Nigel Reo-Coker is apparently still among the living, but that doesn't mean MON will actually play him and as optimistic as I am that James Milner will be on the squad next season, Manchester City are still out there and they still have functionally limitless funds. And as much as I hate to say it, Stiliyan Petrov has entered the decline phase of his career and showed some signs of slowing down towards the end of the year. I don't think Stiliyan is done as a useful regular, but it may be reaching to point where he can no longer be counted on for 90 minutes every time out.
This clearly is not an especially big deal one way or the other; Steve Sidwell isn't a part of the future and he's a fairly insignificant part of the present. He's not likely to fetch a whole lot in a transfer, but he didn't cost very much to begin with and the return would likely be enough to add to the squad's depth at the back. The odds are good that the team are pursuing midfield depth elsewhere, and hopefully they can bring in a player that is a better fit for the squad.
I think that it is important to realize, however, that Sidwell leaving means that Villa are going to need to fill another role on the squad with a player brought in from the outside. This isn't just an issue of Sidwell going away and the team pocketing the transfer fee. If Sidwell goes to Fulham his minutes need to come from somewhere. If that's Reo-Coker, great. I'm skeptical that it will be, however, and beyond him there's really no one on the team I'm especially comfortable with getting regular playing time in the midfield.
I want to stress; I am not opposed to selling Sidwell. I'm just not prepared to say I love it until the move has some context. (Assuming it actually happens, of course.