Polishing goes way beyond 1000 grit, and must be done using a lubricant. This means if you're polishing with sandpaper, you need to wet sand with water. You would also need to work your way from 1000 grit to at least 6000 grit (8-10,000 for the best finishes).
There is nothing terribly special about the Target products - they use the same acrylic resins used by other high-quality waterborne wood finishes, and they can most definitely be polished.
As I said in a prior post, the traditional polishing materials are ground pumice and rottenstone (used in that order) applied with a thick, wet felt pad. The abrasives are available at paint stores and home centers. The felt (3/8" to 1/2" thick) you may need to search a bit for. If you can't find felt, other heavy, smooth-faced fabrics can be made to work.
Stop throwing chemicals at it. At this point, nothing should touch the surface except water or polishing oil. If you need to remove wax (which you will), use only mineral spirits. It will not affect the finish.
Salt water is not corrosive to acrylic finishes. That's why we're able to have acrylic aquariums.
Also, note that waterborne finishes do not achieve full cure for at least 30 days. Until that time, they are susceptible to damage from any kind of alcohol, and may even temporarily become slightly cloudy from water.