Difficult to monetize something that isn't a web app or otherwise requires web access these days.
The shared state model in smalltalk/seaside interests me because sharing state in Django is a huge pain sometimes.
I love how Seaside has changed they way I think about web dev.
Things that can not simple CRUD:
multi step e-commerce order application, games, anything that relies on your previous action to decide what happens now.
a blog doesnt care what I did before, neither does twitter or myspace or facebook. Do this thing, store result. 1 page to result usually. Simple CRUD.
If you do simple CRUD, you probably won't get a ton of value from Seaside/Weblocks. If you are doing applications where stateful is required/desired and RESTful is hard, both will be wonderful to work with.
Django, Rails, Catalyst etc are the end result of a long line in how to do web dev. Seaside/Weblocks/Happstack all break that mold and do something different. The last year of working with Seaside has made me question everything that I knew about web dev after doing it for 14 years. Even if you don't end up using any of the 3, it will have been worth your time.
A bit more, Seaside and Weblocks both offer something similar, given that, I think you should look into trying out Seaside on GLASS which would be a differentiator from Weblocks, although if you are really into Lisp ( I am ) that is a big point in its favor.
In general, I would break it down to:
Seaside or Weblocks on one side and Happstack on the other. If you want to learn, you can't go wrong with any of them.