Just came back from a three week trip to Vietnam with three books: the Lonely Planet, the Rough Guide, and Footprint Handbook.
The Rough Guide is the best guidebook around for the country. It is superior to the Lonely Planet guide in the breadth and depth of coverage and especially its accuracy. I liked LP for other countries but here they did a very poor job.
I have not found even one instance where Lonely Planet provided information that Rough did not have. If you are traveling to the north, you may want to consider reading Footprint before you leave -- it has some interesting information.
Also, all hotels -- even the top ones -- can be negotiated down in price. Send them an e-mail and ask for special rates, corporate rates, etc. You can stay at the Metropole in Hanoi for less than half their rack rate.