I was a amateur ( kind of still am!) and started with a Canon 300D and a 90-300, Every upgrade since then I did for a reason, It might be better if you can also think of a reason why you want to upgrade.
I'll run through mine. I started just shooting for myself, never really planned to send them to papers or anything
Canon EOS 300D( most basic canon SLR you can get for a low price ) -> Canon EOS 20D the AF, FPS and Write speeds were shocking, not good for a sports photographer, the 20D had better AF 5 FPS and a lot quicker write speeds and a bigger buffer.
Canon 90-300 -> Sigma 70-200 f/2.8 I was getting annoyed by the busy background in photos due to the f/5.6 aperture and also the AF speeds/tracking were slow, the 70-200 was a spur of the moment thing, cheap but in good condition and nice and sharp!
Canon 20D -> Canon 1D MKII I upgraded after getting frustrated with my 20D's slow FPS and inaccurate/slow AF, I noticed this one day when shooting a dog running towards me, I knew I needed an upgrade and a saw a 1D MKII at a good price, I ignored the 40D etc cause I knew they wouldn't solve my problem, just make it slightly less of a problem.
Sigma 100-300 f/4 I needed a longer zoom as the 70-200 f/2.8 wasn't long enough, I looked into my option and it was between this and it's much more expensive f/2.8 brother, which I read in some reviews wasn't sharp at f/2.8.
I decided to save some (a lot) money and get the f/4 and have been pleased with it ever since,
Just an example of semi-pro gear vs amateur gear below, I'd like to think there's a difference:
20D 90-300:
1D MKII 100-300
My point is, you've got pretty professional cameras, and you haven't really given a reason why you want to upgrade?