It's my belief that by the 2012 model year Hobie had all the design tweaked enough that pretty much any 2012 and up model is the preferred model to get. They have the Mast brace weld problem fixed, the new stronger glued knuckles on the AKA bars, the larger 3/8 dia bungies on the AMA's, and the newer mirage drives (with the guide pins to make it easier to install the mirage drives. In 2012 they also added the black sleeves in the front scupper cart holes on the hull, fixing the scupper cart problem where the scupper carts were poking through the sides of the scupper holes.
All the aluminum by 2012 (like the AKA bars) was anodized vs painted, and they hold up much better. The new and better rudder system came factory installed (no need to retrofit a new rudder on). Also by then they had gone to the black nylon sail bag for the main sail vs the old silver tarp material (way nicer).
2012 was the best year for the mirage drives, you will likely have little to no trouble with them. On the newest generation mirage drives (2013 and up), they changed the design on the mirage drives and there is a huge breakage problem going on right now (personally I would steer away from any of the newer mirage drives (like the plague), at least until Hobie fixes the problem (and they will).
Look for sun and salt damage on the hull, some tell tales are the four mesh pocket covers in the cockpits, it they are heavily faded it means the boat was left out in the sun too much and in my opinion was not stored properly.
If all the rivet heats have a white crust on them, and the stainless fitting are all rusty, this means the boat was not rinsed off properly after each use in salt water (very important). Also the black anodized AKA bars would look stained and crappy looking. All signs of someone who didn't take care of the boat at all. Though not a show stopper, it should effect price.
The mirage drives should not be all cut up with a salt film all over them and bad rust on the stainless fittings. Also work the pedals and make sure it is not looser than a goose with oval holes on the bearing surfaces (all signs that the mirage drive was abused and not cleaned and maintained properly. The need to be cleaned and lubricated with something like WD-40 once in a while. Though everything is repairable, worn out drives will effect price (somebody has to fix them and repair is not inexpensive).
Open the sail, look for cracks in the clear mylar, and the mylar should be clear and there should be no rips of heavily worn areas in the sail. The sail is the most expensive component on the boat, If allowed to just flutter in the wind it can be trashed in under five minutes.
The hull needs to be inspected carefully for bad gouges and scraped away areas on the bow and tail caused by dragging the boat across parking lots (careless). The bottom of the boat is soft polyethylene and will get scratched even with just moderate use. This is not a problem as long as it's not excessive, most is easily repaired though but somebody has to do the work to fix it up and it takes time, so excessive scratches on the boat affects price also. Always water test the boat before buying. A little water in the hull is normal (none are ever completely dry), but excessive water in the hull (more than a quart) after a normal outing in normal conditions, (ie... fairly small waves (under 1.5 ft), with a few splashes over the hatch from boat wakes, etc are normal conditions), excessive water in the hull are signs of a leak. AI's are typically a little leakier than TI's.
Look at the gaskets in the round hatch covers and the gaskets on the main hatch, if they were cared for there shouldn't be vertical scratches in the rubber gaskets and crud built up around the seals, and they shouldn't look all dried out and brown (the brown is sun and heat damage without adequate conditioning (armorall, 303 or hobie uv protectant spray applied periodically)
My opinion if a 2012 boat is in good condition following the Hobie want ads, it looks like a 2012 TI would go for around .70% to .75% of the current new price.
Actually I see the best deals when buying the boat with the trailer, tramps, scupper carts, and all the accessories included. Basically your buying the whole works (trailer and all) for about the same as the new price for a new boat alone. Trailers, tramps, scupper carts, PFD's, anchors, etc are not cheap and need to be figured and factored in when buying a new boat. Often a great incentive to buy used over new as long as the boat is in good condition.
The TI's design itself is pretty mature, and having that 2 yr warranty isn't as much of a concern as it was in the early model years, where a lot of changes were going on.
We very seldom see hull failures anymore, and Hobie has a very fair exchange program for damaged out of warranty hulls. It's based on age of the boat, and shipping costs from California, in my opinion it's as fair as can be as they can't possibly provide free hulls forever, and the actual number of hull failures from normal use is probably under .1 percent these days. The designs are very mature and reliable (unlike the very early years of Hobie kayaks, where you really needed that 2 yr warranty (I'm sure all the old timers remember all that, not really a problem anymore)).
Hobie's kayaks, adventure boats, and sailboats, plus their service and support are un-equaled and un-matched in the industry (bar none), and worth every penny paid for the value and quality you are getting, and hold their value better than anything else out there.
I have never seen better brand loyalty and support to any other product out there, most every Hobie owner I know would never consider buying anything else.
Hope this helps you