The $150 upgrade is for each additional adult above the single or double occupancy (based upon what you booked). You'd be paying another 10% on top of that in taxes and fees. There are some cash rates that are cheaper than paying for an upgrade. For example, the garden room with club access is sometimes only $200 more than the normal garden room. They don't seem to increase the room price as you can book 1 adult or 4 adults for the same price. I'd be curious to see what they serve in the lounge as I've not come across any recent trip reports. Booking a room for four adults would likely be a decent deal for only $200 extra. Let me know if you end up upgrading. Curious to hear about the experience.