That's complete nonsense. I have no idea who told you that "Liveprep isn't made to stand on it's own." Or that it is merely "high yield topics." You must either work for Kaplan, or have been foolish enough to fall for their marketing tactics. The LivePrep absolutely is enough, but you have to be aware that it is at an accelerated pace, and that you will still have to study on your own after the LivePrep ends for several weeks to months, depending on how well-prepared you were before you started the lectures. If you just graduated, or just finished your second year as a US or Caribbean med student, then LivePrep is just fine. However, if you have been separated from your studies for awhile, or are an older graduate, then CenterPrep is better suited for you. Either way, don't forget to tack on a good online question bank like Kaplan's Qbank or USMLE World, to supplement your book-reading. I love Kaplan, they really have a lot of great programs for Step 1. However, be wary of what they tell you, as they're main goal is to get you to keep buying (and upselling you on) their products...just like any successful business really.
Also, whether you choose LivePrep or the PrepRetreat, be prepared to STUDY. Too many medical students, come to these courses with a relaxed attitude, because they just slaved away for two years in med school, and want to "live a little." Don't get caught in this mindset, study like an animal, and then party all you want once your passing Step 1 score comes back. You worked too hard to slack off now.
Price-wise, the LivePrep and PrepRetreat are basically identical. If you have to buy your own meals, and find a place to live for duration of the LivePrep, then it's pretty much the same as paying for the all-inclusive PrepRetreat. Unless, you live close to the location of the PrepRetreat/LivePrep, in which case you can commute and brown-bag your own food for yourself. And, yes, Kaplan will prorate your PrepRetreat price if you live locally, and don't wish to stay in the hotel overnight as a guest. Even the professors that teach at these lectures are usually the same. Most are excellent, and really know the exam inside and out. Best of luck in your studies, whichever you choose.