The bad WX circuit is taught should a PPL holder unwittingly depart the field into low cloud or poor visibility. Obviously this is something which they should avoid but the reality is that determining cloud base and visibility without a METAR to hand(!) can be difficult for inexperienced pilots. Also, it is another test of the student pilots ability to operate the aircraft in unusual circumstances, similar to the raison d'etre behind the inclusion of advanced turns in the syllabus (for testing pilot skill). So...
Take off and climb straight ahead (oops low cloud/bad viz, etc!) level off at 500' and complete a 180 turn onto reciprocal runway heading until you spot the runway coming back at you. Adopt a close downwind leg and at the end of which complete a 180 turn onto final approach runway heading lowering base leg flap as you turn. Don't forget to make the necessary radio calls but the chances are you're the only nutter up there anyway.
agree with your suggestion about precautionary landings being part of the PPL training, and if common sense prevailed we would be able to use unlicensed farmstrips for this practice, rather than just a field. but we know the common stuff will never prevail, and we will not be allowed to practice this potentially life saving skill.
Not a good idea. Strips frequented by light aircraft should have, at the very least, basic fire cover. Also, it would not be long before popular farmstrips materialised over others leading to the obligatory disgruntled neighbours and an inevitable EFATO disaster. As someone who lives on the approach to a newly made private strip the thought of every tom dick and harry blaring over my back garden practicing PFL's is not a jolly thought. My back garden does not require a mangled PA28 as a new ornament.
VFE.