Your disappointment re: the first class BA lounge in Heathrow T4 is understandable-- as you guessed, it was in the midst of renovation. I am happy to report that it is now open, and one of the best F lounges I have encountered!!! Extremely quiet, a sit down free restaurant (menus with no prices), great work area, etc., etc. An adjacent spa should be finished shortly.

With respect to your attire, as a frequent F int'l traveler, I can assure you that the standards have really changed. In fact, a lot of savvy F class travellers wear old, loose-fitting clothing just to be comfortable (of course, now we've got the airline-issued PJs).