If you have Season 2 of TOS-R on both Blu-Ray and DVD you can compare the episode "More Tribbles, More Troubles". It's on the lone disc dedicated to "The Trouble With Tribbles" (I believe it's disc 5 in both sets). The Animated Series was Remastered in HD back 2006 for the DVD release (which was released in 480/24p Enhanced Definition), and the TOS-R DVD and Blu-Ray sets as we'll as the current complete TAS Blu-Ray just reused those masters. You can compare a True 1080p transfer to a 480p down convert of the 1080p master to see if you want the DVD or Blu-Ray.
Personally, with the TOS-R Blu-Ray, all the 1080p adds is the ability to see the edges of the animation cells. So, for example, in the opening credits, when the Enterprise goes from left to right, I am able to see the edge of the animation cell as they slid the cell across the screen. Otherwise, just like other cartoons of the era (I.e A Charlie Brown Thanksgiving/Christmas/It's The Great Pumpkin) that have had Blu-Ray releases, they really didn't add anything or look better in 1080p than an upconverted 480p DVD, unlike with live action footage.