The Ascension of Jesus, for all the theological problems it raises (e.g."where" did Jesus go!), seems quite important to me, for at least two reasons.
The first reason concerns the significance and universality of the Word made flesh. Jesus ascends (and remembering anonymous' caution regarding the metaphorical nature of our language, and Phillip's comment, quoting Baron, that God is not so much somewhere else but somehow else) to God signifying the universality of the crucified-risen Jesus, the Word made flesh. Jesus is with God, and from here the Father sends the Spirit of God over all the world, now impressed by the crucified-risen Christ. Moreover, this means that the full humanity of Jesus, including his crucifixion and resurrection, is also of eternal significance. Matter is found 'in' the eternal life of God the Holy Trinity, within the eternal, heavenly dwelling of God. (Lots of metaphor here.) The Ascension of Jesus points again to the goal of all creation: union with God in God's own life (through hypostatic union with the Son).
Second, the story of the ascension in Acts 1:6-11 has the disciples looking up into the heavens, even though Jesus has gone from their sight. And then two men question the disciples, the result of which leads them back into the world, back to Jerusalem to receive the Holy Spirit and complete their task as witnesses 'to the ends of the earth.' (1:8) They will witness to the universal Christ, who, in the particularity of his life, death and resurrection, brings universal salvation to all. (Rom 5:18-21) Following the ascended, universal Christ is first about mission.
For all its problems, the Ascension is a beautiful piece of theology.