Thank you a lot for your answers. But I was hoping for a “real” solution.
Over the last weeks almost everybody suggested the static dns workaround for the hairpin NAT problem. Maybe it’s a acceptable alternative for those who have all the services, they want to access from in and outside via dynDNS-address, hosted on one server. But if you have several services on different servers.. a static DNS entry pointing to one of them is not the solution.
Now with the hairpin NAT fixed in 6.7rc1, I tought in works as it should.
What’s new in 6.7rc1 (2013-Nov-08 15:54):
*) fixed hairpin nat on bridge with use-ip-firewall=yes;
Ha 
, while I was writing this post I tested what happens if I set the dst-address of my dst-nat rule to my dynamic public IP (as in the wiki described: http://wiki.mikrotik.com/wiki/Forwarding_a_port_to_an_internal_IP). I was able to reach the server from outside via dynDNS-address, from inside via dynDNS-address and I was able to surf the web. Wow! 
After that I asked google and came across this thread: http://forum.mikrotik.com/t/port-forwarding-with-dynamic-wan-ip/45913/1 ..first I thought I have to tinker this kind of script but the “dst-address-type=local” hint seemes to work, too 
Maybe its not the solution and the next problem is already waiting for me.. I’ll test it and give feedback.