Disabled parking spaces are only one minor irritation for wheelchair users. Let's acknowledge first that there are a lot of ways to be disabled, some of which are not visible. There is a wide variety in mobility for different wheelchair users too, from those completely paralyzed to those who are elderly and need a cane to walk. So someone might be using a disabled parking space for several different reasons.
Beyond parking though, there are the issues of steps, doorways, aisle widths, and so on.
Unless there are ramps, if a building has steps, a wheelchair user can't access it. A helper may be able to pull a manual chair up one step at a time, though that can be dangerous for the rider if anything happens. But an electric chair like mine weighs 300 lbs. Add my own weight, and this chair isn't going up any steps! This means you can't easily visit any friends who live in homes with outside steps.
You can't always put a ramp anyplace it's needed either. For example to get up to a front door with a 6" step, I would need a four foot ramp, but I'd also need four feet for the wheelchair to get started. This is just too tight for safety. So I'd like a 10 foot wide front porch. Ours is only 6 feet. On a related issue, I expect few people give any thought to a second exit in case of fire, but we put a ramp out onto our deck and from there to the grass. (We have a very low deck, and we did have a house fire).
Once you head inside, doors need to be about 4" wider than the wheelchair, and that's a very narrow minimum. Even doors that are wide enough may require an immediate sharp turn. Ideally outside doors need to be 36"; ours are 31" - no wonder there are two big chunks out of the wooden door frame!
Door thresholds are a challenge too, because they can throw the wheels of the chair sideways. We've had to put several mats down at the door I use to go outside in order to get a smooth passage. Commercial door thresholds are usually better.
Once you get inside, you have to able to access things. Our library has an excellent wheelchair entrance, but the stacks don't allow for wheelchair turns at the ends of the rows. I had to back up 20 feet with only an inch or two to spare on each side. You really feel trapped! I've been in stores where you can only get down the main aisles, let alone reach clothes on hangers for example.
Restaurants are a special case. We've been in several, and had no serious issues, but usually the aisles between tables are not wide enough if other tables are occupied. And both the rear wheels and the headrest mount on my wheelchair stick out behind my chair, ready to trap any waitress who isn't watchful enough. Hence my smiley face.
That gives you a rather disorganized taste of what I've been thinking about on our recent excursions. Overall I've been pleasantly pleased by the access we've found, and by the helpfulness of strangers.