Well right off the bat you update all the illustrations so that they gel with what we actually saw onscreen. The contents page also gives a clue to lots of stuff that supposedly should be in the book but aren't, like other Federation ships as well as alien. They could remain as really nice line drawings or they could be as orthographic views of nicely rendered 3D models. I'd be inclined to include some pre-TOS era stuff as well.
I'd also be inclined to rework the listings for all those heavy cruisers. It's just way too many unless you come up with a different design altogether for those extra names. Maybe they could be frigates instead of cruisers. That said you might also consider including movie era designs unless the idea is to keep it strictly TOS era centric (including TAS).
I'd still like to keep the design for the orbital Starfleet headquarters. I find it more visually interesting than the mushroom seen in TSFS.
I like the treaties included because they are referenced in the series. I'm on the fence regarding the The Articles of Federation. I do like the various seals and pennants.