That's a tough one. I used a 50D for a year before upgrading to a 7D, and I've had that for around 9 months. The 7D is the superior camera, without doubt, adding improvements to spec and/or performance in every department imaginable. However, for the birder, some of those improvements are moot, and when coupled to a slow, unsealed, slightly soft, zoom lens I think it is hard to realise some of the other benefits. Also your shooting style will influence whether or not you find certain features important.
For my purposes the advances in AF performance and customisation are the biggest single reason to upgrade, but then I do use mine to shoot a lot of action, including BIF. I also like the 3 stop meter, since I often meter highlights at +3 and to do that with a camera with a 2 stop meter is a pain in the tits. The viewfinder is nice too. In all other respects, while there are some nice to have features, I certainly don't find them to be a big draw over the 50D. OK, high ISO performance is improved, but how often do you shoot at over 1600 ISO? If I'm shooting in conditions like that I would usually not pick up the 7D, prefering either my 1D3 or 5D2 instead. I don't use video. I don't care at all for 8 FPS vs 6.3. The battery life is longer, but it was never a problem in the 50D. I don't use the off camera wireless flash control, although I thought I might, and I don't make use of the level, since that hardly seems useful for an "action" camera. For landscape and architecture I'll use my 5D2 thank you very much. I do make use of the 7D, 1D3 and 5D2, but if I had to wave bye bye to one of them it would be the 7D.
I think all you can do is figure out where you feel the 50D is falling short, and whether the 7D will close the gap for you. Whether the cost to change is good value is down to personal opinion. I don't think anyone else can tell you what represents good value for you.