These questions are fun as you'll get very different and very definite suggestions
So true, @Robo
, so true.
It seems to me that discussing waterproof footwear without addressing the complete outer layer is all a bit pointless. Waterproof footwear might give you some protection against getting damp feet from wet grass and shallow puddles provided you don't splash about too much. Combining waterproof footwear with gaiters or rain pants will start to give lower body rain protection, and with the addition of a hooded rain jacket or poncho, one will get some form of whole body rain protection.
But is that what you need, or want? If you are walking in warmer conditions, you might prefer to walk in shorts or a kilt, when gaiters, combined with a poncho or jacket and rain skirt, might be a perfectly acceptable solution for you. Waterproof footwear could still work for you. But if I were to ditch the gaiters, and let my legs get wet, I suggest that waterproof footwear wouldn't be my priority.
Why? Well someone has already pointed to this, and it is this. Any waterproof footwear has a great big hole in which to put your foot, and unless you protect you legs from getting wet, water will run down those legs straight into you boots or shoes. So with any ensemble that doesn't protect you legs from the rain, wearing waterproof footwear doesn't make sense to me.
Rain isn't the only thing that will get your legs wet, sweat will too. This is where life can get complicated, particularly if you are walking in warmer conditions. If you start actively sweating, this is a sign that your body has stopped vaporising the sweat that it is producing to keep you cool. This will be even more pronounced on muggy days where the relative humidity has increased, reducing the carrying capacity of the air around you to carry off more water vapour. Once you put on a rain jacket, you will start to trap more heat, the rain jacket material is never going to be perfectly permeable, and it won't allow sweat to pass through, only water vapour. Things are only going to get worse!
How long will it take for you to become a walking sweat ball on the inside and rain on the outside, and do you just give up at that point and ditch the rain gear completely? Well, it depends, but generally my take on this is that while it is still raining, keeping rain gear on is still worthwhile if you are keeping your body warm, and you would start to chill if you removed it. If it isn't warm, but it has stopped raining, I would remove my rain pants, and start to dry out my lower body by keeping walking. Only if it is really warm would I start to think about removing my rain jacket.
In cooler conditions, I have walked almost all day in a full rain ensemble before I started to get sweat from my torso running down my legs (and into my boots). When the rain eased later on that day, it took an hour or so of walking to dry of my lower body. The insides of my boots were damp, but dried fairly well with the addition of some newspaper that night. In contrast, on a hotter day, it only took a couple of hours, but in much heavier rain. While my raingear dried off overnight, my boots were soaked, and still damp the next morning, but I hadn't been able to get any newspaper to put in them either.
For what it's worth, I generally wear either leather boots without a waterproof membrane (6/10 pilgrimages) or suede boots with a membrane (3/10 pilgrimages). The remaining time I walked in a suede/fabric boot with membrane. I am pretty neutral to the argument that a membrane makes the boot hotter - that isn't my experience walking locally or on pilgrimage in Europe. I prefer to keep my feet dry, and use foot powder in my socks. I normally walk with liner socks, but walked this year with just outer socks.
If there is any simple summary it is this - if you cannot stop your legs getting wet, there is little point in waterproof footwear.