I've found that lubricating the cable with some spray lube of some kind seems to extend its life. The cables sometimes can bind, making it seem as though they're shot.

On the gauges, I would suggest voltage and oil pressure. You can find both of those gauges in a used 3-gauge pod from an early-80s 240 Turbo for next to nothing. Then, all you need extra is the special oil pressure sending unit for the gauge. The voltage gauge is really easy to wire.

All of this assumes you already have a tachometer, which should be a legal requirement for carmakers, in my opinion.