If you look at the actual increase of weight of a slide, it's really only 2-500 lbs, 500 for a very large slide on the heavy side. The reason is that typically manufacturers remove cabinets and the slides aren't really that deep. A deep one isn't really that much more material. As it turns out, that's about 1 to 1 1/2 foot decrease in length for the same weight. Just think about the "actual" increase in material required.
No hardside camper is going to hold up to real off-roading. Most of the components in a hardside are exactly the same if it is a slide or not. If you think you are going to bend your bed enough to knock a slide out of alignment or break it, you are likely to destroy your hardside wall as well. However, some hardsides like a Northern Lite for example are a completely different design compared to a typical hardside.
By 2005-2006 when I bought mine, most of the TC manufacturers of the time had perfected the slide through several revisions starting around 2000. The newer TC manufacturers like Chalet and Bigfoot who were later to slides are a different story although the people building the Chalet supposedly are the people who designed the Eagle Caps.
I suggest going to the lots in the area and pickout the types of floor plans you really like. For us, we were giving up way too much open space to get a nonside model compared to our Host. But, I'd say that not all slide model floor plans are not as open as ours. If you like hallways, you can get that it in either a slide or nonslide model. Likewise, not all campers have the same amount of windows.
Obviously, the slide mechanism is one more system compared to nonslide models. However, do some searches here and you'll probably find they aren't as problematic as you might think before you do the search!