As is true with most types of design, it is budget dependent. Then, it's a matter of priorities.
There is no debate on whether something is a universal design feature. There are many parameters by which to determine whether something can be considered to be of a universal design application, but there are no certain number of features that should or need to be included in a home for it to be considered functional. In large part, the more included features the better, but there are many factors that affect how many features can be used.
The age of the home, its layout, how it was constructed, the number of occupants, the age of the occupants, the general condition of it now, and other factors dealing with accessibility, safety, comfort, convenience, and enjoyment have a bearing on how much modification can be undertaken and to what degree.
Anytime a home modification is contemplated or undertaken, from simple to major, universal design features should be incorporated where possible. This means that the space will look no different outwardly than it would have without using universal design features but that the entire household, as well as others who might come into the home, will have been accommodated in that space under review and consideration for change.
Now, as far as looking at whether something is or is not a universal design feature just means applying a few simple tests - the ones developed by The Center for Universal Design at North Carolina State University in 1997. Wanting something to be universal design by labeling it as such, when it does not overlay with the main principles, doesn't make it so. This is where universal design is not subjective. In fact it is very objective. It fits the criteria, or it doesn't - regardless of what someone may say to the contrary.
Take for instance a high toilet, the so-called "comfort-height" of 19". Many people include this as essential in making universal design improvements - a "must have" as a minimum set of improvements in order to be considered by others as using universal design. However, it is not universal design at all.
The higher toilet may be a good feature for an aging in place application where the occupants of the home have physical limitations that prevent them from using a lower toilet - or for taller individuals. This is not something that would work for a small adult or a child, however. Thus, it can't be a universal design feature, by definition. Install it at the request of the client, but don't think it will be functional for everyone because it won't be.
As much as we may personally like a design feature or application, if it doesn't overlay the seven universal design principles - eight, if we include the fact that it needs to be unobtrusive in appearance and essentially invisible as being anything special - it is not universal design just because we want to call it such. We can't pick and choose how to apply the criteria or include something just because we want to - it's not meant to be applied subjectively by us to serve our needs.