We have currently booked Temptation Miches, however we have the option of cancelling and booking the grand at extra cost. Is this something people would recommend?
We haven't been to either yet, but we booked for Grand (soon to be renamed Desire) as the price was pretty low and affordable. Booking at Grand/Desire gets you additional access to the Temptation side.
Grand Temptation is more upscale and has additional amenities like bigger rooms and more dining options, but it also costs more. If these things are important to you and you're willing to pay more, it might be worth it. If not, then just stick with Temptation Miches.