On Carnival, we didn't tender at all. I did see one ship, the Seaborn Spirit, parked ouside and tendering. Strange, since it's a very expensive ship.
From what little I know, I'd stick to the ship tours or walking around. Why? Well, first of all, if you return late, the ship doesn't wait. It's your responsibility to find your way the the next port. Second, all of the tours I was on said that cruise ships have priority over non-cruise-ship booking. Meaning, if you want to do something neat, it might be all sold out.
There are some things you just don't want to miss. The shore excursions were the highlight of the trip in Alaska. Cruise ships have to stay, by law, a certain distance from glaciers and whales. Canoeing right up to the Mendenhall Glacier had us wow'ing for days. Heck, I'm still wow'ing a month later.
Seeing orcas doing their mating dance and humpbacks doing bubble feeding was spectacular. More wow'ing for weeks.
If you absolutely cannot afford the excursions, you may be able to pick up some bus tours or walking tours. The Ketchikan walking tour looked nice, and we could have just walked with them if we weren't shopping heavily.
It was the experience of a lifetime, though, there's just nothing like it. So explore it as much as you can afford. It's no time to be cheap. It's worth it.