I purchased an '85 Seafarer with an all teak interior. The PO either liked the untouched look of teak or never put any work into it - it was VERY dry and almost blond looking (unlike the pic above).
I've been using plain old Teak oil, lots of it (4 complete coats so far) and it almost looks like the above pic but no where near as "glossy" (more of a muted gloss) which I like a lot more. Varnish is a whole lot more work!
The way to get varnish that shiny is first to eliminate dust. Second, spray it. There is probably only 3 coats of varnish in the boat in the picture. If you have to brush your varnish, learn to put it on exactly 5 mils thick. Learn to use a wet mil gauge and don't thin your varnish any more than necessary.
I wonder how long it will keep looking like that if it is actually sailed and lived in a bit...
It's really nice, but I am thinking maybe its a show boat. It like cars. They can either look great, be really fast in the straightaway, or handle through the twisties really well, but rarely all three... Oh, and then there is the daily driver.
One of the real keys to acheiving that level of gloss is to level the finish by sanding between coats and using a very good brush. On things like furniture you can even polish the finish to gloss by using VERY fine sandpaper and then polishing compound, though I think spar varnish would be a bit too soft for that.