I'm so glad we booked this! It's worth the price to have your own guided tour with someone as knowledgable and friendly as Valentina. The crowds and queues waiting in line can take your breath away (and I'm not even referring to the heat that can exhaust you).
Once you've had the luxury of skipping the lines, it's great to relax and listen to the wonderful Valentina (yes she's amazing!) give you interesting anecdotes of the museums and the masterpieces in it. We got the most interesting history lesson ever on the museum, the art and sculptures.
Don't take your chances of waiting in queues because on the very rare occasion you got through quickly, you still would miss out on important facts behind the artwork, which of course means you probably wouldn't appreciate the work in there as much as you could (unless you are an art or history major)!