Hi Ian!
Until I toured The Netherlands in 2008, I had not seen 3/4 tights (they called them "knee tights") in general use for cycling. They looked to be the perfect solution to keeping my knees warm without overheating and I managed to get some upon my return home to the States. Looking online, they were common here for women, not men. The situation was reversed in the online European shops. Now, it seems the rest of 'Merka has come 'round, as they are a common sight for men on our bike paths. Much of cycling is fashion-driven and it can take awhile for trends to catch on locally.
I have chosen to have (synthetic) chamois padding only in my cycling shorts, keeping all my tights padding-free. This way, the shorts become my base-layer and I can don or doff the tights at will and remain decent for passersby. Riding on two pads was "two much".
The unpadded tights can be tightly rolled and secured with nylon-covered hairbands (longer life and no snagging compared to rubber bands) to take minimal storage space in my HB bag or panniers or even a jersey's back pocket.
It does help to try on several different models. I've found there is a sweet-spot between too long (constricts my upper calf) and too short (keeps crawling upward. You definitely don't want fabric bunching up behind the knee, and a common sweaty spot. If the fabric is too rough there, it can cause some irritation on long day rides. For some reason, not all 3/4 tights seem to have the traditional cyclists' "cut" (higher in back), so that is something to watch for as well. Not as critical when work over cycling shorts, but still convenient to have.
Overall, 3/4 tights work well for me and have become a staple in my cycle-touring wardrobe.
Best,
Dan.