Yeah, I have been thinking along the same lines in terms of how much weight it can tow. I am putting in a 1.6 td motor, and will be using an electric brake system on the trailer I am towing, and maybe adding more springs or air bag assist to strengthen the back. But, I'm with you, I don't think I want to pull more than the weight of the caddy, although I will see how much my trailer weighs and see how it pulls.
GeeBee has some good ideas for brake mods which would add the estra stopping power needed for more weight. 
Dennis, any of the trailer hitches sound useful for your application?
Most seem to need a bumper to bolt to. Im looking for something to bolt to the rear spring support boxes. I will probably wind up building one. I probably won't tow anything heavyer than a lawn mower or tiller. the trailer I bought is only 4x6
Dennis, in that case - I have a trailer hitch mount bar that came from an 84 Jetta. Pretty sure it mounts up in the way you describe. Non-dependent on a rear bumper.
I'll get it out and see how/if it mates with a truck structure.
Give me a few days on that though.
You no got no rear bumpy ?