Heill Gordon!
You mention "producing a text."  I assume you mean "writing" in the archaic language.  My question is Why on earth would you want to write (what?  letters?  short stories?  critical articles?  a novel?) in an archaic language?  Who would your audience be?  Certainly a very limited one.  If your goal is to learn to read, you certainly don't need to learn to write, as well.  If I have a choice of spending a half-hour doing an exercise that helps improve my ability to read Old Icelandic or doing an exercise that helps improve my ability to write in Old Icelandic, I will certainly choose the former.  Remember that we are not talking about modern languages here, but about archaic ones, languages produced by cultures that no longer exist.  The culture that produced Old Icelandic texts is "gone with the wind."  The Vikings are no more.  So why, except for kicks, would you, or anyone, wish to write to them, e.g., letters, or for them, e.g., stories?  Much more productive and interesting to learn to write in modern Icelandic and to modern Icelanders, no?  And to do this as efficiently as possible, one would need to study the grammar, syntax, vocabulary, and culture of modern Icelandic rather than Old Icelandic.
 

[Christian Bartel] 
I somewhat got your point... but I cannot really distinguish between reading and understanding. Of course I read English in a way you described... I guess words from the context without actually translating them... But that seems to me a very enhanced state of learning a language, no? In the beginning I would have to look up anything to understand... and so it might be easier to know the structure of the language... That might help me to guess a lot more words...
But I understand that there is a difference.
 
And: I actually want to produce text. You can believe it or not, but I am inside a group of german viking re-enactors and we try to reach a point of making the language of a use again (at least on some events). Next to that we try to play a viking-thing in the original language (with translators for the audience). That should give them an impression of the vikings that is much better (and it is fun anyway) :-)
 
Of course we are at the beginning. For the last year (where the thing took place the first time) we learned all the text by hard and that will be pretty much the way we are going to do it this (and the next) year. But maybe one day we have a couple of people who are able to actually communicate (very simple matters) in the original language. That might sound completly crazy, but it is really fun...
 
 
I hope that this has clarified the issue somewhat.
 
well, yes :)
 
 
Þor blessi þig,
    Christian aka Meldric