Eliminate thy marketing budget!

Most software companies I speak with continue to have a set marketing budget that covers all of their expenditures. To me, this is a sign that they are probably not measuring the effectiveness of their campaigns.

If performing any given campaign is generating great leads, and these leads are reliably converting to sales, shouldn't they just keep increasing their spend so long as it generates sales? Why place a limit?

It is my opinion that a set annual marketing budget should be eliminated. Instead, two separate budgets should be created:

1) A set budget for experimenting with new marketing channels (that are unproven in their ability to generate leads) as well as media that are viewed more as brand building rather than lead generating.

2) A steadily increasing "budget" for campaigns that have already been proven to work. The only reason to cap these at all is to account for the lag between the initial point of contact with a potential sale and collecting money from am actual sale.

Placing an artificial budget on a lead generation activity that is proven to work is one of the surest ways to limit your growth. Thoughts?