The catch-22 of chassis weight is too heavy and it can make the motors work too hard/heat up, make the tires wear out quicker, and drain the batteries faster. But a heavier car with weight low on the chassis will feel a bit more planted into the track.
You might consider something like 1450 grams as a minimum weight, which is what the USVTA rules are for their cars. This weight would allow heavier and/or older chassis cars to be more competitive without putting them on a huge weight diet. This would also allow some of the tub chassis cars to be more competitive. However some of the newer chassis might need to add weight.
I would think the goal of a minimum weight in a class such as this would be to discourage people from spending crazy amount of money and/or time on lightened components. However if the bulk of the racers are using lighter cars such as 2wd pan cars (200mm pan cars), then the weight rules may need to be a bit lighter.