In my opinion, there is remarkably little that has changed and improved. I should perhaps also say I have a '98 motorhome and am quite content with it, so I may not be entirely unbiased in my opinion.
The typical RV appliances have not changed a lot over this time period. Stovetops, absorption fridges, gas RV ovens, water heaters, furnaces, air conditioners, generators, and water pumps are largely unchanged over this time period. Microwaves may be slightly more powerful or more likely to be microwave/convection combo units. Cabinets and furniture and fixtures are generally similar, though perhaps differently styled. Decor in RVs seems to consistently be ten years or so out of date.
The Ford E-series chassis has not a lot of change over this time period, either, beyond a steady but slow series of improvements to the engine and transmission. The newest 6 speed transmissions are, at least on paper, a more significant improvement than most of the previous ones, with a significantly nicer gear spacing. (The difference between the four and five speed units is basically just adding a gear between first and second and, probably more importantly, improved programming.) Older Ford engines have a design issue that make them comparatively prone to ejecting spark plugs.
What is likely to be different and possibly of importance are the entertainment systems, the number and size of slideouts, and the availability of a few features. Older televisions, without a digital tuner, cannot receive most all of the television broadcasts today, and CRT based units are much bigger, heavier, and more power hungry than modern LCD units. Replacing them in an older RV makes a whole lot of sense. (The antenna systems still work.) In the newer features, perhaps the most common are outside kitchens and outside television sets.
Build quality is probably roughly the same on average, though it does vary from make to make and model to model and is often none to excellent. Newer units may have the advantage of having less chance for poor or missed maintenance. Some early slide mechanisms (and some not-so-early ones) were not as trouble-free as might be hoped.
If you want a unit on a newer chassis such as the Sprinter or ProMaster, it obviously can't predate when those were available.
