Sooo, to bring this thread up again in 2021.

I had the same problem with random crashes without error, but for me it wasnt 30min, it was 5 min.
i also had the problem, that when i played the game and loaded a savegame after some minutes, i could not even spawn any addon car because the trainer "coulndt find model".

I did the same with the ambient sound stuff and deleted it, but i got some crashes afterwards.
i uses this guide to try some stuff link text

i left the textures on super high but disabled and reenabled the vsync again.
i have around 30 addon cars, ALL the addon wheels (like 500) with all the textures, i got 10 replacer cars like the mule, the jet (a380) goodyear blimp. i also got natural vision evolved installed and all the textures for roads and billboards pack and everything. my DLCs have a combined size of around 10GB of mods. and it does not seem that this is the end.

so anyways for the people who read this in 2021:

-delete ambient car sounds
-lower graphic settings and do the stuff in the guide
-update graphics driver
-update gameconfig, heap adjuster etc.

helped for me atm )