Which Holiday Inn will you be staying at? The way they name the hotels is so crazy. The Holiday Inn ACROSS Universal is the closest. We walked over to pick up a rental car one trip and another couple of trips, we have stayed at the Doubletree Suites right across the road. That one is about a 10 minute walk. Longish, but doable along a nice sidewalk. We usually stay there after staying one or two nights onsite.
Our last trip, I accidentally booked Holiday Inn Express nearest Universal. Well, this one is about 15+ mins walk away. Still manageable, but definitely further. There is a shorter cut that takes you to the Orlando Ale House and I suspect it is a shorter walk if you cut through that way. The street was a little odd though and it didn't entirely feel like we were walking the right direction the first time we tried it. On the good side, this hotel has free breakfast. My kids were super intrigued by the pancake maker - they hadn't seen a conveyer belt-style one before (and neither have I!).
Depends on what kind of person you are. I could see a week's vacay at Universal quite easily. It would be a more relaxing pace than Disney though since you are right - there isn't quite as much to do at Uni. But then, we are the kind of people that can spend 3-4 days straight at Cedar Point and still have fun
Still, you have a very valid point. After 3 trips (each staying 3-4 park days) to Universal with our Power Passes, we are just about done. We started feeling like we were running out of things to do on our last park day. That's partly because we aren't big Potter fans though and we have by and large skipped Forbidden Journey since our first trip.