What a wonderful dilemma!
i have also been on many Med cruises and have loved every second of them. Only one in August as I was cruising with one of my sons who was still on school, the others all in May or October. August is really hot but we found it tolerable. We had a two week out of Barcelona ending in Venice with only two sea days. Also stops in the Greek islands and Turkey. It was a great introduction for my son who saw all of the highlights in just two weeks but port intensive cruises need more planning and we didn’t do much of the nightlife on the ship.
i agree with all the other posters that you should not leave the Med for too long. It is demanding and strenuous if you want to hike in Cinqueterre, traipse around Ephesus of Pompeii. In August, half day tours would probably be the way to go. You can do dozens of Med cruises and discover different locations every time.
We have also been to Alaska, it is a wonderful trip. It was not on my bucket list but had some flights we needed to use or lose. We chose an itinerary that went up North and a b2b down. Excursions are costly but well worth it and we were in awe of the scenery. Demographics seemed to skew a little younger that I expected and is less formal. Lots of jeans and outdoor wear. To us it seemed that we would return to Alaska when we were older and would just enjoy the scenery and the ship as not much culturally.
Seize the day and don’t wait!