Here is my perspective.
My first DSLR is also a 5D Mark III with 24-105 f/4 L and Speedlite 600ex-rt. I can afford to buy this system, and am learning very quickly from my mistakes and from when I do get it right, which is happening more often now, but I still have much to learn.
If I had bought a 650D, then I would make the same mistakes as I have with the 5D Mark III, but in the shots I do get right, I would have more noise, less depth of field and with slightly softer images (assuming I would not have bought an L lens to keep within a tighter budget).
I believe I get more keepers with my 5D Mark III as it one of the most well balanced DSLR's around with very few faults.
No it will not make you a better photographer, but you will likely get better results when you get it right, have more keepers and quite simply enjoy using it.
I would not discourage any newbie from buying it, should they have the budget to do so.