Is the lake so unique that there are no lakes that actively compete with it? Since you have lake front lot sales (it seems), were they on the same lake?
Marketing lake properties is very seasonal. Now is the time the "tourists" come out and drive every road on the lake looking for that rare jewel. You cited a 2013 listing, but depending on your market, that may be irrelevant at this time (my market has gone bonkers and we wouldn't want to use it as a base here).
For lake properties, it is not all about the front footage, but very much about the lake and position on the lake, as well as the quality of the frontage itself. I wrote an article about my experience appraising on Michigan inland lakes a while back, if you want to read it:
http://www.workingre.com/appraising-lake-property/