I had gotten into paper modeling via the thought that paper designs might work as templates for scratch building plastic card models (it's all 'card', or thin sheet material, after all.) Well, that can indeed be done, but often the paper model is just fine as is. I like lots of fine detailing, so I tend to add stuff using whatever material can do the job. Just depends on what your personal modeling 'goals' are as to what you do with the media you're using.
I can say that paper modeling is a real challenge and requires a whole different (though somewhat related) way of thinking about the build. This fact alone makes attempting a paper model a valuable experience (I say attempting because it may take more than one try before you're happy!) I've come to believe it doesn't pay to be too pedantic when it comes to materials - as long as it gets you where you want to go. Sometimes this translates into using the same techniques repeatedly simply because they work! However, if you find yourself in a rut, opportunities exist to expand your horizons, with paper modeling being one of the most economical & varied in choice.
A perfect example of a 'fusion' project is a F7F Tigercat being built in 1:18 [actually, 1:24] scale & documented on Britmodeller.com Forum. The model started as a paper model, which was then 'filled' with expanding plastic foam, coated with (essentially) Bondo putty, has had various sections cut out (such as the cockpit) & reconstructed using various materials to a high degree of fidelity, and now is being 'plated' with thin aluminum (not foil, but thin 'plate'.) It is a wonderful piece of work, very interesting to see - but all based on the paper model's original 'template'. I recommend checking it out (and wouldn't be surprised to see it in a modeling magazine somewhere....)