Two tips to prevent blisters from walking in sandals: spray antiperspirant on your feet, &/or use Body Glide. For our feet it is good sport sandals all the way, absolutely no sneakers, and no flops, either. (Wet sneakers ... ugh.)
On days when it is rainy or if we are going on rides that get us wet, we also wear technical clothing that dries quickly. We still do ponchos, but we don't need them except in major downpours. We keep the cheapy ponchos for the entire trip, and then we give them away to other guests who are waiting for wet rides. We store them in a ziploc when not in use.
Of all the environmental conditions that make me feel miserable, being wet while fully dressed is at the top of the list. Chafing from walking around in wet street clothing is awful, so investing in sports clothing is worth it to me.