Hi Glenda, long time no see!
I have only sailed once since the excursions became free and it was in Alaska. Pretty much the same excursions available as my previous Alaska cruise on Regent. I would say they are just as good as they always were. Several of our excursions, it was only the two of us from the ship so I would say ours weren't overcrowded ;) Excursions in Alaska are very $$$ so we saved close to $700pp.

As for which ship is better, The Nav tends to vibrate aft, not sure if the SS ship does, lol.
Free internet on the Nav, which is a bonus for me.
As you say, the no formal nights is a bonus for us too. Not that we mind getting dressed up, it's just too much of a hassle to pack tuxs and suits and drag them along.