I went from a Rebel XTi with kit lenses to a 5D with L lenses.....trust me you upgraded.
The Rebel is a great camera for what it is, but even with the grip it's too small and the 10d on up has a fuller feeling in the hands, everything fits like a glove. You upgraded.
Plus I'm not sure what the shutter rating on the Rebel T1i is but I know the 40d is something like 100k or 150k exposures. My XTi was 50k and I blew through that in a year. Just finished replacing the shutter.
What matters most is the glass. You can have a Rebel XTi with L lenses and it will take a better picture than an EOS 5D with a kit lens. I'm actually writing up a comparison between the two soon to prove that good glass > good body.