Also, a hitch step-up
You reminded me.
If the vehicle has a hitch receiver, you can get a retractable step-up that fits in the receiver square. Businesses that sell truck and 4x4 accessories carry these–also check Cabela’s automotive catalog. If I remember correctly, there is even one with multiple collapsible steps, for greater height.
Another Hullavator vote
I agree that they are pricey, but they make loading sooooooo easy. They rotate the hull to the side of the vehicle, allowing the hatch to open completely. They allow you to easily snap on the cockpit cover. They allow you to pop gear bags into the cockpit or hatches.
With the Hullavators the most awkward move is kneeling down to release the latches before raising the boar.
Jim
Last resort
This thread wouldn’t really be complete without someone suggesting a trailer. On the positive side, very easy to load/unload, avoids cost of most of those fancy loaders/unloaders, only on your vehicle when needed, no boat scratches on your vehicle, no overhead clearance risk, less wind drag, space for additional boats and gear, may provide boat storage space, useful for non-boating chores. On the negative side, parking hassle, requires backing up skill, two more tires/bearing sets to maintain, small license fee, some areas may have reduced speed limit for vehicles pulling trailer.
Side by Side
My wife and I have a Pathfinder which is not very different from an Xterra with respect to roof size. We use Thule cross bars and saddles and carry our kayaks side by side (how long are your cross bars?). When we had a Perception Shadow and an Eclipse, we used a RollerLoader to help us shove the boats (bow first) onto the rear saddles, but when we replaced the Perception boats with a Wilderness Systems Tempest 165 Pro and a Tempest 170 Pro, the RollerLoader wheels were too far apart to use with the new boats, so now we drape a towel over the rear saddle and the wind deflector, and slide the boats over the towel, onto the rear saddle and from there forward.
Try it; you might like it.
Wheel Steps
For comparison between Thule and Malone, I found this site which has the Malone Wheel Step.
I have not used either so can’t give much info on how good either work.
http://www.maloneautoracks.com/accessories.html
cheaper…
to buy a box to stand on… 
J Frames
It seems to me that any kind of a side loader, or J-Frame is not a good idea for a solo person loading a boat unless you are 6’6" and strong as an ox.
There is just too much height to overcome since the boat has to be lifted above the cradle. Crawling around on steps is dangerous.
I load my Ford Ranger with cap easily because I can slide the boat up, and on.
I raise the bow of my Tempest to the side of the bar(padded) and then move it to the center of the bar between the saddle pads.
I then go to the stern,(protected with a piece of carpet padding) and push the whole mess up, and forward.
BTW, I’m 5’9" and retired!