The sagas abound in obsolete vocabulary, things that are never said in spoken language today and unrecognizable to Icelanders without a commentary. Icelandic is conservative in some vocabulary, due to a decision since the 19th century to revive some old words and coin new native terms instead of borrowing from other languages. However, plenty of other old words fell by the wayside. It makes no more sense to read the sagas in preparation for a trip to the modern country, than for a foreigner to read Shakespeare or Chaucer in preparation for being a tourist in the UK.
Also, don’t expect to speak Icelandic as a tourist in Iceland. The local people are well known for keeping aloof from tourists (tourists most often interact with a foreign workforce brought in from Poland etc. to serve them), and unless you have already gone through a course of the language that has prepared you to handle a full conversation, they will simply immediately switch to English; otherwise they would feel you are just wasting their time.