There are not a lot of guides for these countries, though perhaps one guide per country would give you more detail on each, and/or be more compact. It's not clear to me that anyone going to one of these countries would probably go to all three, especially since most Westerners go for business, or to live in one of these countries in the long-term.
Nonetheless, given the paucity of travel guides for the region and the less than developed tourism industry in Georgia (the only country I have visited out of the three), the Lonely Planet guide was invaluable. Lonely Planet has a lot of problems - few photos, difficult to read black and white maps, and a lot of worthless practical information (post offices, laundromats, etc), the descriptions and histories of the sites and neighborhoods was better than anything I would have gotten within Tbilisi, in English.
Georgia is a country in transition, so certain information was a bit out of date, particularly any area in or near the conflict zones. Can't blame Lonely Planet for unexpected wars. I had the opportunity to travel quite a bit in Georgia in the course of a week or so, with Georgians. Four out of five sites were well covered in LP, with good history and descriptions.
So, if you happen to be going to Georgian and don't speak Russian or Georgian, this LP will make your trip much better.
On another note, Tbilisi is a very lovely city surrounded by high hills and a large ruined fortress looking down into the city, with some of the nicest people I have ever met. I have had problems in many cities, "Western" and developing, where people were either rude, con-artists, outright thieves, or harassing. In Tbilisi people were welcoming and honest - even the taxi drivers! And if you are American, and afterwards an EU citizen, they tend to love you because of the events in August 2008. It's just sad that such a nice city is so far off the beaten path.