Anyone sent their gauge cluster to get restored?

When a speedometer is new the fitment is so tight that no amount of cable pressure would cause erratic or noisy operation initially. Pressure from cable causes wear and subsequent issues. In some cases relieving cable pressure can get proper operation for a few more years. I can't know how much wear is in yours.
Speedometer restore alone will go 200 and up. There are some tiny naval bronze bushing in them. Inventories of good used parts are surely depleted today. If they don't have machinery to make those parts they have them made, probably in lots/runs of 100 pieces. I shutter to think what that costs.
Not much to the thermal gauges (fuel and temp'). The heat is their enemy so a full tank of fuel and how it responds every time the switch is cycled is shortening the life of the fuel gauge. I would expect it to need renew. On the other hand, your temp gauge may need no more than bench test calibration check, screen cleaning, and needle paint.
If you do buy into the amp gauge to volt gauge conversion, you will have some rewiring to do on your end, in the car, because they are totally different in how they connect to a circuit. I suppose Red Line/whoever would provide guidance in that.