It depends on how 'SPD' your 'SPD' shoes are: I have a pair of SPD's which I use for commuting, geat on a bike, not so good for walking, and another pair of Trainers with SPD fitting, perfectly good for doing city type walking.
If one is going to do hiking, then you want heavier boots, trainers of any sort are downright dangerous on mountains
So assuming on your tour you are only doing city type walking, you only need one proper pair of shoes, which you use on the bike as well.
You take along a light pair of sandels as well, quite useful for wandering about camp sites in the middle of the night, and to give your feet a bit of fresh air whilst setting up your tent and cooking.