Tom, if you'll be more specific we can really help you with a "do-able" experience in a short stay, & keep you from disillusionment on a deceptive "island cruise" which is mainly at sea, with rushed stops at ports, surrounded by other cruisers.
First, do you already have fixed DATES, not just "mid-late May". And are you required to be in Athens for business immediately upon landing? If not, and you have at least 6 days, you can have a good one-isle experience PLUS athens, by being travel-efficient. Us "old Greece vets" recommend getting a domestic flight ASAP (Allow 2 hr layover) to an island like NAXOS or PAROS for 3-4 days, then returning to Athens for the last part of your stay -- since u should be there the night before departure flight anyway. Another option, depending on what day/time you arrive, would be to catch a ferry on arrival day to a beautiful island such as SIFNOS.
It is hard to advise someone, especially so close to a trip, when so little info is offered -- it would help if we knew age range and desired activity (do you hike, or prefer cafe-sitting?), interests (scenery - nightlife - ancient history/ruins - shopping?). Your concern about ship decor perhaps being outdated may indicate more interest in upscale surroundings vs. wandering thru villages ... but we can only guess, unless you share more. One thing though -- April is VERY late to make transport & accommodation bookings, so PLEASE supply specifics to get the best advice... we want to be helpful.