Here is a link to the articles in the Austin-Statesman, regarding the value lake front properties. You might have to create a login to access the articles themselves. Nothing in the articles really speaks to the value of land over time.
As for value, it depends on what you define as waterfront. If you mean land abutting navigable waters, then don't use the Austin Board of Realtors definition of Waterfront, which includes everything from a dry creek to Lake Travis. Presuming you mean land abutting navigable waters, then the data indicates that since '04, for lot values alone, many areas, especially those on Lake Austin, Travis and along the main tributaries, have increased in value well over double since '04.
A lot of the value increase depends on many factors. If the land has been improved, that is, it has a home on it, then the larger the value of the improvement, the less likely it is that the property is double it's value from '04. More likely, improved land along the above shores has increased in value less than 50%, primarly 2004 was our coming out year from the slow times of '02 and '03, so values were on the rise. If you asked the same question from late '01 or '02, I think you could see well in excess of 50% increases in value for improved land.
The land by itself though, in most instances, has clearly more than doubled in value. In fact, depending on the lot's access to the water, whether the land permits building above the newest high water level, how deep the water is that can be accessed directly from the lot, whether or not the lot would allow a boat dock, and if the lot has a view, some locations have seen a 3x to 4x increase in value as the supply becomes constrained.
Are you curious because of a tax assessed value issue, for the value of selling your home, or just curious in general?