It sounds like your planning on a lot of travel. That means durability. The construction of your Casita, reduces the number of likely roof problems, it is fairly aerodynamic, it is relatively low in height and light in weight.
Moving up to a standard TT construction you gain room and conveniences but you also gain height, weight and maintenance. There is no doubt that an Airstream would be a good choice and closer to what you are used to but you are talking big bucks.
If you are not in a hurry, I would rent a trailer of a size and layout similar to what you want for a week of towing and parking. It is expensive, but as they say; education costs. It will give you a real feel for gas mileage, towing, your TV capacity and a host of other intangibles.
I would look for a good used unit as new TTs depreciate rather quickly.
Good luck and keep us posted.
