1, You can always texture reflection strength. If you put any bitmap in the reflection color slot, then it does not override reflection level value, but reflection level value defines maximal value of the map in reflection color slot. So for example if you have reflectivity map in reflection color slot, and reflection level set at 0,6, white pixel on the reflectivity map will have maximum value of 0,6 reflectivity ;)
2, Fresnel is there to keep material physically correct, if you want superreflective material, then set diffuse color to pure black, reflection level to 1, and Fresnel IOR to something like 100 ;)
3, I don't think so, it would break energy conservation therefore it would break pretty much entire renderer ;)
4, That's an ugly fake. Corona is primarily designed to be fast physically plausible renderer with some amount of flexibility, but we are not making another MentalRay. The less fakes - the better performance. If your entire workflow is based on extreme flexibility, then i can only suggest you stick with the renderer you have been using up until now...
If some fake features will be heavily requested, then we will try to add them eventually, but we would also like to ask you to put some effort into changing your mindset and trying to work in a more realistic manner, with as least fakes as possible. You will be rewarded with more realistic results as well as maximal available performance potential of the renderer.