Sorry; I wasn't as clear as I thought I was. Absolutely, I think you should wear your glasses to train as a general rule. But, occasionally, you should train without them. Free sparring is not a good exercise for this; that's why I said one-steps or similar controlled extercises.
In the same vein, most of your training will be in the dojo or a similar environment, wearing a uniform and with a good warm up. Occasionally... move out of that comfort. Wear old, "normal" clothes. Train outside. Skip the warm up and see what happens.... Of course, if all your after is some fun or a sport to do, you can skip this stuff, since it's only really relevant to self defense.
I hear you and agree. I have been thinking a lot about doing SD exercises, even kata, in street clothes and shoes outside on uneven terrain. I think it's a terrific idea.