I consider a re-release as "original" when it is the exact (or very close) replica of the original (sometimes re-released with the same reference). These re-releases may include minor alterations like adaptation for modern battery packs, replacement of the original mechanical speed controller with an electronic unit, stickers modifications, material or color changes on some parts, or even parts modifications in order to make the model more reliable than the original used to be.
Overall, the re-released model is provided under the same form that made its success years ago. Re-released models complying with this criteria are sorted in order of appearance of the original model:
58004 XR311 Combat Support Vehicle (2000 / 2011)
The model was first re-released in 2000 and again in 2011, each time under the same reference as the original's (excepting the change in kit numbering): the re-releases are strictly identical to original, except metallic torsion bars on the new versions, the battery tray that was adapted to receive modern 7.2v packs and a minor modification on the bodyshell for the antenna tube mount.
To my knowledge, this is the model Tamiya chose to inaugurate its re-release program more than 10 years ago (either "as per original" or modernized form).
58015 Rough Rider (1979)
58441 Buggy Champ (2009)
84162 Buggy Champ Gold Edition (2012)
84187 Buggy Champ Silver Edition (2012)
When re-released, this model lost its original name. However, "Buggy Champ" might have been the original name of the model in Japan (like with the Super Champ re-release). Other minor modifications include sponsor names and minor chassis aspects.
58016 Sand Scorcher (1979)
58452 Sand Scorcher (2010)
Alike the Rough Rider / Buggy Champ, minor changes can be found on sponsor names and mechanical aspects of the chassis. The bodyshell was a bit modified too (closer to the Monster Beetle's).
58038 Subaru Brat (1983)
58384 Subaru Brat (2007)
84237 Subaru Brat Metallic Special (2011)
The re-released versions mainly differ on mechanical aspects to make the model more reliable (gearbox) and by replacing the original Mabuchi 380 motor with a 540.
58034 Super Champ (1982)
84389 / 47304 Fighting Buggy (2014)
Alike the Rough Rider and Sand Scorcher, some modifications were made for this model re-release, but the original spirit of the model is preserved. Two things worth to mention: the original photo with the rims painted in blue or red comes from the 1983 RC Guide Book. The next catalogue issue presented the Super Champ with a more conventional decoration.
"Fighting Buggy" is the original name under with the Super Champ was released in Japan in 1982. So the same may apply to the "Buggy Champ" re-release of the Rough Rider. Kits number 84389 and 47304 are strictly identical.
58041 The Frog (1983)
58354 The Frog (2005)
Same as the Brat re-release : modifications mainly focused on the gearbox to make it more reliable.
58043 The Grasshopper (1984)
58346 The Grasshopper (2005)
84331 The Grasshopper Candy Green (2012)
84416 The Grasshopper Black Edition (2015)
47348 The Grasshopper Candy Green (2017)
There is no difference worth to mention between the original and the re-released versions. As for the two Candy Green versions, only the kit number is different.
58045 The Hornet (1984)
58336 The Hornet (2004)
58527 The Hornet by Jun Watanabe (2012)
84383 The Hornet Black Metallic (2014)
There is no difference worth to mention between the original and the version re-released in 2004. The 2012 version is technically the same but its look is somewhat... different. As for the 2014 Black Metallic edition, it is a limited series coming with a pre-painted bodyshell and black rims.
58046 Fast Attack Vehicle (1984)
58496 Fast Attack Vehicle (2011)
58539 Fast Attack Vehicle (Shark) (2012)
Some parts from the Wild One provide a better reliability to the re-released versions. The "Shark Mouth" edition did not exist in the 80's.
58047 Hotshot (1985)
58391 Hotshot (2007)
84265 Hotshot Metallic Special (2011)
Despite many parts replacement on the re-released version, the model still keeps its original form.
58048 Toyota 4x4 Pick Up Bruiser (1985)
58519 Toyota 4x4 Pick Up Bruiser (2012)
The 2012 version is a faithful re-release of the original Bruiser since the bodyshell is almost identical (now accepting LED installation) while the chassis is slightly reviewed, especially on the gearbox side.
58050 Wild One (1985)
58525 Wild One Off-Roader(2012)
There is no difference worth to mention between the original and the re-released version.