Points to consider...
* The shutter counts provided by Canon are estimates of average lifespans. A 1DX might lose a shutter at 10,000 images, while your T1i still clicks at 250,000. That wouldn't be the average, but it certainly can happen and will happen to someone. Don't assume your camera is about to die based on shutter count.
* The 5Dc is definitely better at high ISO then the T1i.
* The T2i / 60D / 7D out perform the 5Dc in all respects, including high ISO / noise. This is a tested, measured, and proven fact for those who want to argue that "FF must always be better!" (See the reproducible tests at DPReview and Imaging Resource.) The differences are small, but in the crop sensor's favor.
* A used 5Dc will have a shutter count equal to or worse than your T1i.
* The 5D2 / 6D has clearly superior noise, sharpness, and fine detail at ISO 1600 and above over the 18 MP APS-C bodies. Add to that superior fine detail at any ISO over the 5Dc. How important this is depends on what you do. 8x10's at 1600 and 3200? It's a non-issue. ISO 6400, 12800, and/or 16x20 high ISO prints? You will definitely appreciate the 5D2 or 6D.
* If you absolutely need the high ISO performance (i.e. >3200 and/or lots of 16x20 prints at ISO 1600 and above), your budget only allows for a used 5D2.
* If you are leaning towards the 5Dc because you also want a new lens, you should be looking at Canon's 18 MP APS-C bodies. (What crop glass do you have btw?)
* Unless you get one really cheap, it's hard to recommend a 5Dc that will have just as much wear and tear as your Rebel, and fewer features. It is better at high ISO then your Rebel. At the right price it could be a good move with your budget and a lens. But every time I check the 5Dc's they are overpriced because people think FF is "magic" when it's not. At any price I've seen them, the 60D is a far better option.