I want to improve my technique with tripods. Do most people add weight to their DSLR kits to get them to perform better with video tripods? I'm wondering if lack of rails is causing problems with my footage or if its the weight of the kit.

More than likely its the head itself. Many inexpensive heads are not particularly smooth which will hinder your efforts. You can try adding weight--you don't need to use a baseplate and rod system specifically, you can just use a steel plate between the head and the camera. I'm sure they are out there for sale but I can't point you to them--any machinist can make you one very cheaply.

I'd like to know the answer to this as well. What happens when the camera is BELOW the tripod head's rated payload? Is that a performance neutral issue? I don't want to be adding steel plates to my tripod. The Lumix cameras all weigh about 1 pound and most tripod heads don't rate from below 2 pounds. So far the Sachtler FSB-2 and 4 and the Libec RS250 seems like one of the few options. I don't see this topic addressed much in any of the web forums.

I talked to Chuy at Libec today. He said for DSLR shooters, unless you can get your rig to 4lbs or more, the Libec RS-250 or the LS-38 are an unwise purchases because you are paying for features you won't be able to utilize, such as CB. He recommends this one Libec-LS-22DV (http://www.libecsales.com/products/dv/ls-22dv.html).
Very affordable actually at around $350 from B&H.

Sachtler's CINE-DSLR head is rated for 1-11 lbs.