While there were beautiful renders done with P4, they did not include features the OP is looking for. And just like any other computer grpahics, the old renders do show thier age today. My old Amiga and Atari 800 did some outstanding graphics as well, but compared with whats available today, they look primitive, and simplistic.

The OP wanted to do mirrors, and found that he could not. Now he also wants effects like ambiant occlusion and subsurface scattering, and those require the newer render engines.

It sounds very much like he's outgrown P4, as almost everyone else has, and Daz Studio is free, and can offer advanced rendering features like mirrors without paying a penny.

While P4 was great in it's day, if I had no money at all to spend on software, I wouldn;t be using it,  I'd be using Daz Studio, not P4. 

Rather then spending time trying workarounds that just aren't what he really wants, he could be investing that same time learning the advanced features available today for free.

Way too many people take way too many things way too seriously.