I had similar issues, and I've rebuilt a significant portion of my Polaris 280 for less than $200, over the last month. It was slow and didn't climb walls well, and upon inspection I noticed was that the teeth on the wheels were worn out, so I replace all 3 wheels, and put on new bearings. I also noticed that the axle was worn down on the edges (it looked beveled, when it shouldn't be), and when I pulled the axle out, the part of the axle that looks like a watermill (the part that drives the axle) was nearly broken. Just replacing those items made a significant difference. The float head had water in it, so I replaced that as well. The backup valve seemed to malfunction (water spitting out when not supposed to be engaged), so I replaced that. My hose keeps getting twisted, so I ordered 3 new swivels, and hoping that that solves all my problems.
Once I've replaced the worn down parts, it cleaned the pool well (until the hose started twisting, which is why i'm replacing the swivels), and I'd rather not spend $500 on a new robot. It's not difficult to repair/replace the parts. 3 swivels cost me $25, as opposed to paying $125 for a whole new hose. I did notice that my pressure relief valve is blowing water, but my wheels are getting the requisite 28-32 RPM, so I guess the pressure is just higher than needed. I ordered a blue and red disc, and will see if that helps.
The 280 is easy to work on, and if you are like me and don't like unnecessary spending, you could probably fix the polaris yourself. All you need is a phillips and a flat head screw driver and the parts.
