Not saying you guys are doing anything incorrect, but I have had best results with linseed oil and mineral spirits (combined). Teak oil and other mentioned products have given me darker results over the years. This last time around in 2012, I used the linseed oil mixture and I'll not go back to teak oil or other.
Took me two coats and my board looks primo....
Your boards look fine and the teak and Starbright will weak down in a few months of lake use, so consider the aforementioned concoction.
If you're not 100% satisfied, I'd consider stopping where you are and use the board until it needs another treatment, then try the linseed oil/mineral spirits. Several folks here have the same or similar testimony of which I speak.
I'm not sure what sanding gets you but it's not my board to say. Most of these slicky-boy finishes are for show and IMHO, not practical for use, but that's me. I like functionality. I pressure wash my board once a year, no sanding.