People complain about more control all the time. That's why there is more and more people saying how complicated Vray is. You have very specific workflows, so you should be the one going the extra mile to achieve that super exact specific task you do. If there was was a button for every specific thing someone does in their workflow, even as simple thing as AO map would have at least 200 knobs.
First of all, if you do at least moderately complex materials, you should definitely start using slate editor, if you don't do so yet.
Other than that, there are just so many ways to do what you want, not only mix node. You can simply use RGB offset in your map to change intensity of the map if it's in the white slot, or RGB level if it's in the black slot.
Seriously, in Vray there are as useless things as redundant GI/Refl/Refr multipliers in matte settings that even Vlado himself is not happy about. Adding bloat into UI is not one way thing. It's not a gain without any expense. It's always gain in accessibility at the expense of UI cleanliness and organization, therefore ease of use.
It doesn't make workflow any slower, it just requires some change of it. So when you plug say a bitmap in the slot of AO map, and that map doesn't give you exact result you wan't, and you decide you need to modify the result, it's just a matter of going at the different place than you are used to. Instead of going to AO map to adjust map influence spinner, you stay in your bitmap, and adjust level or offset instead.
