I am not a cruise person but a cruise to Norway would appeal to me more because seeing the fjords from a boat must be quite unique.
As to the weather for your Spain/Portugal trip, the later you go the more unstable the weather 'can' be but generally you should be fine. I have travelled several times in (southern) Spain first half of October and have had a bit of everything but usually it was ok.
One of those 2 week trips started in Seville where the weather was great, after in the Aracena mountains the weather started changing and by the time we headed to the coast in Huelva and Cadiz provinces it became rainy and very windy, but that's the Atlantic.
Another 2 week trip around that time was in the south east, Almeria to Murcia and interior. While there had been extremely heavy rains and floods in the whole area just a couple of days before we left (still visible when we were there with damaged bridges and deviations), we couldn't have had better weather with temps around 28°and blue skies during 2 full weeks.
All in all i wouldn't hesitate for travelling to southern Spain first half of October again, but given the distances and the various regions you are going to cross, you better expect some variation in the weather as well. And one year is not the other. Also, your trip is mainly focused on cities and large towns where i think the weather is of less importance (except when they are too hot in summer) compared to the countryside/mountains/Natural Parks or if you would be heading to the beaches.