With all respect, I'm not sure that your stated desire to move up to a full-time 5th wheel is compatible with a SRW truck as a tow vehicle. Our Mobile Suites (see signature) has a 19,000 lb GVWR; the same model in Elite Suites trim with the same frame and suspension has a 21,000 lb GVWR - that is definitely dually territory!
If your wife is comfortable towing with a SRW pickup, then she will adapt easily to towing with a dually. We've been towing 5th wheels with Ram duallies since 1996, and my wife is quite comfortable driving the truck either when towing or around town after we arrive at our destination and unhitch the 5th wheel. The rule of thumb she uses is, if the mirrors will fit, then the rear fenders will fit. It's just a matter of getting used to it.
As far as your original question, we traded in a 2004 Mobile Suites 36RE3 that we had owned since new to get our 2014.5 Mobile Suites 38RSSA. I'll be retiring at the end of this year, and we decided that we didn't really want to go into retirement with a 10 year old 5th wheel, despite the fact that it was in excellent condition. The newer MS had features that weren't common or available on the 2004 such as disc brakes, automatic leveling, residential refrigerator, etc.
If this will be your first 5th wheel, I'd recommend buying a used full-time rig and use it for a few years; you'll quickly learn what you like and don't like about your choice so that when you buy that next 5th wheel for full-timing, you'll have a "must have" list based on your personal experience. Seldom does the first 5th wheel, despite how nice it looks on the showroom, meet all your expectations after you've lived in it for awhile - our first 30' single slide 1996 Jayco Designer 3030RKSS was great until we took a 2 week vacation. By the end of that vacation, we both decided that it was just too small and claustrophobic. We kept it until 2000 when it was replaced with a Jayco Designer XL 3610RLTS.
Rusty