
I too had thought of some of the same ideas for grinding the inside edge of each rail. I think SteveM's idea of a mounted grinding wheel could work with the aforementioned feeler stop, which I would just rest on top of the rail, but long enough so that when it goes over a joint it still stays consistent with the average top surface of the track. Then some kind of adjustable height. It pretty much just needs to be stopped from digging in when you stop. If you have an electric loco with a good speed control, you should be able to set it to a nice consistent, very slow speed and let it run around the track.
Regarding broad gauging - yes only if you have tighter curves or longer wheelbase engines or combination of both, otherwise you can get away with a consistent gauge throughout. On our 9" gauge 3" scale Mesa Grande Western railroad, there is no gauge expansion around curves, and our minimum curve on the mainline is about 60 feet. Our longest wheelbase loco is a consolidation with blind center drivers, only the front and rear drivers are flanged. (see pic)
Most 7.5" gauge railroads I visit regardless of rail type slightly broad gauge the entire line. The Bitter Creek Western Railroad is 7 5/8 rather than 7 1/2. This helps prevent very large engines from climbing over the rails somehow even on the straight sections. The problem it is fixing is a result of poor wheel profile design on the part of the IBLS draft standard, which actually was trying to show the minimum flange height and radius, rather than the desired flange height and radius. IBLS flanges are too small and the radius too small for conventional radius top track profiles.
Regarding flange to tread radius, if you have a decent radius on the track, then making the radius on the wheels slightly larger will prevent flange wear as the track will find the part of the radius nearer to the tread first and keep it away from the flange. If the wheels are steel and the track is steel with a proper radius, there shouldn't be too much wear in that area.
What can really prevent wear is a properly set up pilot truck. A friend in New Zealand (where all track is essentially groovy track - no affordable profile rail exists over there) recently added a pilot truck to his Kerr Stuart prototype. They adjusted it until the side springs kept the front driver flange 2mm away from the outside rail on a 60ft radius curve, with the result that there should be almost no wear on the front driver over time, just have to periodically freshen up the pilot wheels, which is a lot easier. Previously it was experiencing a lot of wear as it is an 0-4-2 that is used in heavy passenger service on most weekends. Now it is a 2-4-2.
Attached is a picture of the 9" gauge Mesa Grande Consolidation, on a 65 ft radius curve and a side view at a crossing to see the wheel arrangement clearly.