I've been reading about the political & economic philosophies of Henry George.

So far, I like it. It's the only philosophy I've found so far that merges my libertarian feelings with my concerns for the environment and labor. It is embraced by Georgist libertarians or 'Geolibertarians'.

The short version.
The value of land is not due to the effort of labor or industry...it was endowed by it's creation, and value added to it through the efforts of the community...land in a city is valuable due to it's location as a center of commerce, etc. No ONE person has a right to this value, it should be returned to the community, in the form of taxes or land 'rent'. Contrast this with the fruits of labor and industry as shown here. Henry George was a proponent of the Single Tax as the source of revenue for government.

In reading Georgist websites, I often find links to Green sites, much more so than Libertarian sites.

Is this philosophy viable within the existing parties?

In my opinion tax on land would now be a regressive tax, things have changed since George's day. No longer do the wealthy, have, or need to have, a substantial part of their wealth tied up in land. It seems this plan would tax unfairly middle and lower class homeowners who have little assets besides their home and the land beneath it.

The land 'rent' is the appreciation in value of land. It doesn't reduce the value of the land, and it is not assessed on improvements. For example, in an area with 8% annual real estate appreciation, George recommended returning 95%*8% = 7.6% of LAND Value to the public coffers.

This would have the net effect of developing high-value land, reducing housing and transport costs, both significant expenses for the poor and middle class.

Furthermore, the rich tend to own more land and more high-value land, taking a larger percentage of their income. I can't find a link now, but I've read that 40% of the value of Fortune 500 companies is Real Estate. Land Value Tax wouldn't devalue those holdings, it would merely end the effective appreciation of those lands, encouraging those companies to put the land to productive use, or sell them and invest the value elsewhere.

If, by some wave of a magic wand, all existing taxes were replaced by land-value-tax and user fees, the poor and middle class would greatly benefit. Profit from land appreciation would be returned to the public good, profit from capitalism would be returned to the capitalists (encouraging more investment), profit from labor returned to the employees.