As far as "unique," well it depends what you want to do with it. If you're going to heavily modify it, then anything is possible. You could buy a rust bucket with a blown drivetrain and swap in an entirely new running gear or a diesel swap, etc. or toyota axles or even a Samurai front SAS...or chop it up into a buggy...
Depends on your needs (and wants) (and budget).
If you're going to flat tow it, I'd recommend (IMO) manual hubs...I bought one with auto hubs and bought aftermarket manual hubs. It will help relieve stress on the CVs when you're flying down the highway with the Tracker in tow. Also a twin stick to disengage the front driveline (since "neutral" still locks the front/rear drivelines together), and you'd gain 2LO too.
If you plan on installing a low range gearset in the t-case, look for 91-98, or else you'll be in the same position as I am in, looking for a donor case of the proper year to install a gearset since mine is a 1990.
If you plan on doing such stuff in the future such as HD driveshafts, which require a SYE, Trail Tough is the only company I recall who makes a SYE and it is for "fine spline output shaft" cases only...which I believe is up to 94 and some 95 models. Skyhiranger knows about these specs, he's advised me in the past.
If you're looking to add bigger tires, and later on, probably swap gears to match the tires, you MAY be better off buying an automatic. I have a 90 with the 5spd, so I have 5.12 axle R&P. My only upgrade options are 5.38, 5.62, or 5.83. Two of those are very rare OEM R&P that you MAY or MAY NOT find in a junkyard. The 5.83 is offered by Richmond Gear but IIRC they are taking pre-orders before they make any more at this time. And the list is very short, too, I think.
In your situation, if you buy a Sidekick or Tracker with an automatic, your gearing options are much better. If you get a 4spd auto, your axle ratios are 4.62...then you can upgrade to 5spd gears (more available). IF you get a 2dr with a 3spd auto, your ratios are 4.30...and then you have the option to upgrade to 4.62 (4spd auto) or 5.12 (5spd) gears, which both are more available than the 5.38, 5.62, 5.83.
Sidekick Sports came with the 1.8L. Kind of a "rare" engine (not as common as all the 1.6L 8v and 16v running around) so parts may be hard to find, wrecking yards too, and aftermarket support is something to consider. I think some of the parts are interchangeable but not all of them.
If you're going to work on turbocharging, talk to bentparts about his 16v, or wildgoody about his 8v. From what I've read, the 16v is better suited for this, but don't take my word for it, talk to these two guys, they're experts. Not to mention there's several more turbo'ed people on here too
This is all stuff I've learned about in the one year I've owned my Tracker and been a member of this site. I know I won't be the only one to reply here. If I'm wrong about anything here, guys, please correct me!
And yes, there is such thing as a two-door, 4x4, convertible model Suzuki Vitara and Chevy Tracker. Don't know much about those models, though. They look pretty damn awesome. Bigger engine options, too.
I didn't know this, but there's a tintop model, too (it's on the "reader's rides" of the GV forum, 2nd page or something like that).
If I had the chance to get another one, I think price would determine a huge factor. I like 5spds, but a CHEAP one with an auto is still a CHEAP one nonetheless.