I'm going to bump this.
Armor all is supposed to deflect UV. You have to keep this topped up. The only way a dash can crack that i can think of is if it been neglected before or after you apply it. Armor all should be used to prevent drying and cracking. No point after the neglect is already there as moistening dry and cracked vinyl will accelerate old damage. You can't flog a dead horse type of thing. A little tip: never spray directly onto the dash around your vents etc as it will pool in all the grooves etc and attract dust. Spray it on a microfiber cloth first, then apply. You'll be able to use that moistened cloth everywhere.
I was at Supercrap Auto the other day looking at duco care products. I've used
Carnauba wax products for years. Some older vehicles which looked like the paint was so far gone it needed a respray I have cut and polished and they have ended up with a glass finish. When their this bad, I used to use one buffing pad for cutting, clean it and put it aside, wash the car, then use a new real lambs wool pad to polish in the wax (all done in the shade). We decided that when buying new vehicles, using paint protection offered by Toyota and some others that claim to be miracle products such as Silica, all needed to be maintained by washing with the same product such as a Silica car wash. These companies claim wax attracts dirt and contaminants and traps it in the wax itself, but regular washing and re-application every four to six months of a good quality Carnauba wax and wash was not only more satisfying to use when you see the end result, but also cheaper in the long run. Other paint protection companies claim wax melts when it gets hot. The warmth and pressure of the buffer machine does a good job of applying it and I've not had any complaints with steering wheels on the road in a puddle of wax and no car around you. Good orbital buffing machines can cost around $600 and fit specialized pads suited for the finish your after, but this is for prestige or show cars really. A two speed Makita will set you back about $245 and with quality pads and a little care in using it will give you a nice finish too. I only need something to buff in the wax and keep using the wash as mentioned above. You can buy cheap buffing machines for $45 which don't have the power behind them, but if you take your time they will also do a good job as well. Another tip: remove any plastic protectors. You don't want to accidentally hit them and break them off.
I think paint protection is a rip off and many people get suck into the pitfalls of maintaining those expensive products. Even ARB recommend you seal the powder coat on their bull bars with Carnauba wax.
Meguiars is an excellent product. Turtle Wax made a Carnauba wax product called Excalibur. I have not bothered to see if it still exists, but I also recommend it as a cheaper alternative.
Wax ooonn, wax offf.
Shaker.