I'm a recent convert to FF. After using a 30D for a while, I picked up a cheap, used 1Ds mkii late last year. As mentioned by others, there's noticeably less Depth of Field when shooting with wide apertures and you are generally shooting with longer lenses. Combined these help to give images more "pop". Photo's from the new camera seem to have more of a realistic / "3D" look. Colours seem "better". The photos have more detail. Of course, this could be due to a lot of things - my imagination and twice the megapixels being the main things that come to mind. But overall, I definitely prefer the photos from the FF camera. In my first week with it, all I can remember thinking was "Wow, I should have grabbed one of these earlier". Even now that the initial excitement has worn off, I still think that there was a big quality gain by changing cameras. And given that my camera is 7 - 8 years old, I'd have to assume that a newer FF camera would be even better.
Now, that was going from an 8.2mp crop camera to a 16.7mp camera. I'd like to think that the sensor in a 7D would be significantly better than a 30D and the increase in megapixels to a FF camera isn't as big. But there would be a slight difference. Given that you'd have to change some lenses and buy a new body, you'll just have to decide if a minor gain is worth the price.
A simple, cheap experiment - Pick up the cheapest working Canon film SLR you can find off ebay (maybe $15), a projector ($20) and a roll of Provia ($6). Take some photos and project them onto the wall. That's what FF versions of your photos would look like. Do they look better? If so, make the switch to FF (then sell the film camera and projector and get your money back).