I think a lot of modders can agree to that one, and especially roleplay based servers as you added. Thankfully we've started seeing more attention on new functions concerning model side of things over the years.
Definitely check out TheNormalNij's contributions towards the (WIP) new vehicle system through the page that Dutchman linked. You can also find him often talking about the subject in our Discord at #development.
For the meantime there are work around's that I'd consider worth trying, though their hit on performance may vary so be mindful of that. For objects, you can replace many of the ~70 casino duplicate models and ~14 Liberty City cutscene models, which already adds up to nearly 100 ID's available to replace.
You can also add multiple meshes to 1 world object by utilising opacity shaders. Say you have a grass block and a dirt block, each using 1 texture. You can then hide one of the blocks by applying an opacity shader to the unwanted texture. This works best with meshes that share same collision, or collisionless entities like weapons. You can then attach these weapons to a game weapon and hide the base model, which is then overriden by the world object which has multiple meshes - ideal for weapon customization.
The same applies for vehicle and skin models. For vehicle models though, you can set the unwanted components position to below the world so that it isn't seen. I've heard people using this method for tuning systems.