Funny enough, I was in your situation exactly - a 30D and a 50 1.4
Here is the way to look at it:
1. The people who say that glass is a better investment than bodies WERE correct, because in the past digital bodies were a new technology, while glass was mature. That meant that spending a large amount of money 5-10 years ago on a digital body was an expensive proposition, because digital bodies were evolving so quickly that what was state of the art became run of the mill very quickly, and the value dropped fast. The same thing has been (and still is) happening with memory cards. You can get a memory card for $50 now that was $500 very recently. But digital bodies are maturing now, and we won't see the huge advances in a short period of time like we did in the past. From now on, we are likely to see fine tuning and subtle refinements. Many who are buying the 5d3 have stated that this will be all the camera they will need for the next 10 years. In other words, it's a lot safer. (Canon knows this, which is one reason why the price of new glass is going up, and they are charging decent margins on the 5d3 and 1dx)
2. The 50mm 1.4 on a full frame is a very different lens than a 50mm 1.4 on a crop. Not just a wider angle, but also a shallower depth of field. This will apply to every lens you are thinking about buying.
3. Everything is relative, the gains for someone shooting a 5d2 may not be worth spending $3500 on a 5d3.
The gains for someone shooting a 30D will be enormous, and you will therefore benefit more from the leap to the 5d3.
4. Do you need the pro AF and faster fps for your shooting style/subjects? If not, perhaps a 5d2 and more pro glass will net you more returns for the same investment. Remember, going from a 30D to a 5d2 is still a huge jump
5. You won't see someone running around with a 1dx and a crap lens....it doesn't make sense. At some point, if you haven't already reached it, it won't make sense for you to be running around with an arsenal of L glass and a 30D.
There will always be new cameras coming out in the future...there will be a 5d4, and then a 5dV....but if you wait for Canon to announce their "final" model, you'll be waiting forever. There has never been a better time to buy a FF camera, and you have more than 1 option. It's not 2004, and your new body will not be worth half of what you paid 12 months from now.