I have just returned to Norway after a year backpacking around in Latin America (of course accompanied by the Lonely Planet books). I do not claim to be an expert, but I know what I look for in a travel guide!
This edition of the LP Central America did not disappoint me. I used it, going from Panama to Guatemala by bus(!). It is up to date on the information, and as with all the other LP books it is easy to find your way around with it. It includes maps over the big cities, good information about the hotels, restaurants, places worth visiting, and time schedules for bus, train etc. You have to take into account that this is a guide that is meant to cover the whole Central America so naturally it is not as detailed as the guides for each country separate. It is good as an overall guide if you plan to go to more than one or two countries, as you would try to cut down on the baggage to carry around.
As for the prices for hotels and food, the book is fairly accurate.. It is hard to keep up with all the changes, especially in the Latin American economy, where the inflation is "somewhat" higher than in the rest of the world. So, for prices - if you are on a backpacker-budget, do your own research, or at least be prepared for changes! (We usually multiplied the prices in the book with 1,5 and that gave us a good indicator of what to expect).
You will find that if you are walking around with the LP book under your arm, many of the local people will approach you and ask you if you need help. Say yes - even if you don't need help! It is a great opportunity to get in contact with the local people!
This book is a must on your travel!