There is a lot of difference with the car.
Chassis:
The chassis has been significantly extended. It is cut differently at the front for the new side guards.
Three of the mounting holes for the front of the chassis have changed leading up to the center diff/slipper. The first hole for the servo mount is no longer countersunk; the new servo mount used a pin instead of a screw for the first mounting hole. The front two mounting holes for the side guards are several millimeters back to accommodate the new side guards (you will not be able to use the new side guards on a 1.0 without upgrading the chassis).
The mounting hole for everything after the diff/slipper has been shifted back but looks to all be the same (my guess is it’s dependent on the chassis length; the -3 chassis is likely 1:1 to the 1.0 chassis besides those 3 holes mentioned earlier).
Steering is all the same.
Servo Mount:
Completely new. Looks like it would fit, but I didn’t try it. You’d likely have to drill a hole in the 1.0 side guard to get the servo mount to fit.
Center Diff/Slipper:
Mounting holes are all the same. DC, no issues; exactly the same as 1.0.
It will likely be difficult to swap to the new Decoupled slipper in a 1.0 car. New front mount that requires the new servo mount to be used. Might fit using the same tricks to get the AE decoupled slipper to fit.
Shocks:
The shocks are almost all new.
Shock ends, shafts, caps, and x-rings are backwards compatible with the 1.0.
If you already upgraded to 13mm shocks (AVID, or another brand), there is no point in upgrading. If stuck on the 12mm, the 13s are noticeably better.
Shock towers are different to accommodate the diff height adjustment of the new gearboxes. The mounting holes are the same, so they should fit the 1.0. The 1.0 Shock towers will not fit a 2.0.
Arms:
The arms are redesigned. The front arms are now a Gullwing style. The rears are the same but have a different molding to accommodate the 22x.
Both are backwards compatible, but you will need a -2 front tower to maintain droop for the front arms.
Roll Center:
The ABCD blocks are the same, besides the new blocks C&D blocks on the AC.
If you have the Vision Racing C&D blocks, they are the same as the new AC C&D blocks.
New front castor block, only difference is it’s adjustable. It should be backwards compatible.
The sway bars are new but using the same part number.
The turnbuckle rod end and ball ends are larger, but are backwards compatible.
Diffs:
The ring and pinion of the diffs are the same. The pinion appears to be of higher quality than the 1.0.
The diff cup is different but should swap into the original gear box with no issue.
F&R Gearboxes:
The #1 question is the 1.0 gearboxes have been discontinued for some time.
The gearboxes are backwards compatible, but require a lot of additional parts to fit.
You’ll need the following to get them to fit:
It’s a lot but still cheaper to keep your current car running than buying a new car. On the bright side the new gearboxes are a clear upgrade over the original car.
If you’re running a DC, it could be economical to slowly upgrade it to a 2.0 hybrid. Especially if you’re running on loose dirt and not high-traction clay, then the big upgrade to the extended chassis won’t be worth it.
If you’re running on Carpet/Astro, it’s likely best to get the new car. Unless you’ve done the AE decoupled slipper mod and Vision Racing +5mm chassis, the gearboxes and arms will get you 90% of the 2.0. Otherwise, there is too much, and these upgrades are ones that make a night-and-day difference on an AC car.