Yellowstone

best to plan on 4 days if you want to take in all the major walk arounds and visitor centers (there are several, each one focused on different aspects of the park)
I suggest taking a picnic lunch with you each day so you can save some money and also stop and eat when and where you feel like it.

You didn't say when you will be there. We have traveled there in the Winter and the crowds are not to bad so there are no traffic delays. We also get up early to be at the gates when they open. This is the best time to see wild life from our experience. Without crowds, we spent three days in West Yellowstone. This gave us plenty of time to explorer all of Yellowstone.
If you plan on going there at a time when it is crowded, I would add at least one more and maybe two days to be able to see everything. There will be times when you are just stuck in traffic and can't go anywhere. If there happens to be an animal near the road, you can sit for a long time before you move again.

At least two days, three would be better. One thing to remember about Yellowstone, is you won't be going any where very fast. You have to get through the gate each day. Roads will be congested, time you park and walk around, to see stuff, it all burns time. The actual distance between stuff is not that far, on the map. But the actual time to get anywhere and do any thing is quite a bit longer.

Grand Canyon, unless you are going to ride the train, or do some hiking is more of a one day thing. And it tends to be over run with tour buses, not something I enjoy being around. Just talking about the south rim, not the north rim or the sky bridge etc, which of course would take longer

The OP stated he would be driving into the park each day.

My advice: Forget costs, a long drive daily just to get to the entrance will suck all the joy out of the visit(s).

Bryce and Zion are once in a lifetime thrill.

Kerry

We have never stayed LESS than a week and still see something different each day. You need at least 5 days to see all the main and side roads once, so plan accordingly. West Yellowstone is a good base, as you will see different animals every day as you head to Madison junction to begin your day.

Just some figures:
From West Yellowstone to Madison is about 15 miles.
From Madison, the bottom loop is 96 miles around and back to Madison.
From Madison, the top loop is 84 miles around and back to Madison.

I would think at least 2 days per loop might get some highlights.
We generally stay a week at Madison and a week at Mammoth Hot Springs.

Geeze WyoTraveler, he said he'll be staying at West Yellowstone. You can do the south loop on one day and the north loop on another from there. I usually spend 5 days to see most of the attractions. Consider seeing Bryce and Zion on the way down to the Grand Canyon. I would also stay a night at the north rim and then go down to the south rim. If your wife would like to check out indian crafts go out the east entry of the Grand Canyon to the little Colorado river where a number of vendors set up.

Driving into Yellowstone from where each day? There is a lot of driving in Yellowstone. But from the gate to your spot may be an extra drive. Just for an example: Gate to Cody is 70 miles.