I am not sure that baking a relay at 100C and then measuring coil resistance is the best way to choose the pullup current, although that would definitely be one way to do it. I was hoping that there was a generally agreed upon range of contact currents that avoid dry switching problems.

Oh no, Lee, you missunderstood me. Sorry, I don't have a better english... My idea was to look for that relais (of those many you have in your car), which has maximum coil resistance. So, may be there's one relais in your car that has 300 Ohm, or so. That was the idea, but not to put it in your toaster... {grin}
But, with your new information, that car must run in desert, situation looks different now, anyway. From friends of mine living in Tunesia, I know, that desert sand can become extremely fine. And when you worry about contact problems of relais caused by sand, then I would also worry about contact problems of driving switch!!! Are your switches so well sealed, that absolutely no sand (dust) can penetrate?
Wouldn't it be a good idea, to also change switches? Then you can use special types allowing dry switching and drastically reduce driving power. There are types on market guaranteeing IP67 for switching mechanics.

You told about disadvantages of relais. Most of them are right. But, low impedance of relais coil is also very helpful in preventing mistriggering from noise or EMI, just because coil resistance is so low ohmic. Don't underestimate that point. So, when reducing driving power, your application becomes more susceptible to EMI. In this case some simple low pass filter -at least one capacitor- at input of your solid state switch might be very helpful.

In another post you stated, that fuses can be neglected, because solid state switches have protection circuits. Be very careful, fuses are NOT ONLY used for preventing damage from failing relais, but also from short-circuits of wiring!!! I would NEVER, NEVER, NEVER omit fuses! Equally how save everything might be.

Is there any possibility to have a look at one of your racing cars? I'm highly interested...

Good luck,
Kai