My first and second DSLRs were also the 500D and 5D2, it was a great upgrade, build quality, handling, image quality ... everything except the AF (no, that's unfair, the 5D2's center point did really well in low light compared to the 500D) and frame rate. And yes, many lenses will behave better on full frame, although it depends on the lens and the criterion, for example vignetting is less of a problem with a crop sensor because you are not using the more-vignetted borders of the image circle.
The more I read, it seems that crop bodies have a singular advantage over full frame and that is the increase in focal length.
At the beginning it looks like an increase in focal length, but really you are just cutting away ("cropping") part of the image. The only advantage of crop sensors that is sometimes (!) relevant (except for price) is actually the higher pixel density.