Buy the aircraft that A.) best fits
your mission and B.) best fits
your desires. Looking in my logbook I see that my solo time outweighs my pax hauling time by 4 fold, and few if any of my pax have ever found a ride in the back objectionable... Of course not all pax are built the same. MY smarter half likes riding in the back just fine and I have no problem flying from the back when I want to give someone a different perspective.
Having said all that, I have flown several tandem aircraft that were almost as wide as a sxs and therefore IMHO didn't really offer a whole lot of benefit to the tandem arrangement.
The baggage deal is never as sweet in a tandem, but you must compare apples to apples. Tandems are 2 place aircraft... How much more are you really going to get in a 2 place sxs of equal size and performance? For the rv4 guy I would suggest that a T-18 Thorp is a sxs similar in size and mission, and will probably carry less than your rv-4, and I can assure you that the seating arraignment is no where near as comfy as your RV... You surely can't compare the baggage of a supercub to a 4 place C180, but I am certain that my 2 place cub will pack more than a 2 place C150, and do so more comfortably, both performance wise and passenger wise....
Equally true, I have flown a good amount in a well equipped 2 place bird dog, that would haul much more than the average 4 place 172, and did so on a fairly regular basis.
As for pets, most of the cub guys I know have dogs that fly with them on a regular basis. I don't think the dog knows the difference between the front seat or the back?
Nausea? looked at the ball lately? the back seat of anything is not as kind as the front. Be kind to the sensitive ones and you'll be ok, better yet learn to fly from the back and offer the front to the most sensitive... they will love you for it!
I think the sxs is going to be a more universal airplane most of the time, for most folks. But if it isn't the right airplane for you, you will either regret going that way, or end up cashing it in for what you should have bought in the first place
Just more opinions to confuse you with
Take care, Rob