I totally agree with the negative comments about a sundeck cruiser. Another is if you plan on doing a lot of fishing, or scuba diving, it's more difficult with a sundeck.
That being said, our boat is similar to a sundeck cruiser, in that the aft deck is raised about 5' off the water line. However, having a large swimstep (ours is 4') mitigates a lot of the negatives.
Several advantages we've noted, one of which is pretty obvious, is that the aft cabin is huge, and full beam! Great for a liveaboard.
The second real advantage we've discovered, we found out by chance last year in our trip to SE Alaska. When others in the anchorage were getting eaten alive on deck by the noseeums, we weren't bothered at all. My take is that the Noseeums tend to hug closer to the water, and with the deck being 5' out of the water, they didn't come up that high, but I may be wrong. We were in the same anchorage, same distance from shore, pretty much same everything, except for "altitude" above the water, and the other two boats were getting eaten alive, and we weren't bothered at all! Also, we tended to have a little more breeze than the lower cockpit boats.
Either way, if all other things were equal, being a sundeck or not would not decide me for or against a particular boat. Best of luck in your search!