If you are very interested in plants you would rate this higher. It was a relatively short stop - as the area is not too large and easily walkable. The plants/trees were well marked and viewing and photographing them was relatively enjoyable.
Mendenhall Glacier Rating:
Combined Rainforest gardens, Mendenhall Glacier and State Museum tour. The tour included two of the highest rated sites (glacier and museum), only took a few hours and was relatively inexpensive. You could do these 2 on your own with the shuttle to the glacier and a moderate walk to museum and save a few bucks. Mendenhall is impressive and there is a lovely waterfall (via a moderate walk) as well as a nice visitors center. The State Museum is also recommended as it gives a very good overview of the native cultures, gold mining history and information on wildlife, geography, etc. We also walked around town and visited the unimpressive Capitol Building (with a self guided tour) and the outside of the Governor's Mansion and, of course in town shopping.