Yet another Mir's first happened early in the station history. When the very first flight, Soyuz T-15, visited the station on March 15, 1986, just weeks after the base module was delivered to orbit, cosmonauts didn't stay aboard Mir the whole time. On May 5 Leonid Kizim and Vladimir Solovyov left Mir in their spaceship and flew to Salyut-7, where they arrived 29 hours later. They run a set of activities there - including two EVAs - took 350-400 kg of equipment from Salyut-7, left back for Mir on June 25 and arrived there in 29 hours.
This was possible because Salyut-7 and Mir stations shared the same orbital inclination - though flew at different altitudes - which allowed to spend a modest amount of fuel for transfers, and Soyuz spaceship had enough fuel. For future space station it might become important to have that capability - if something happens on the station, and crew needs to evacuate the station, and another station is within reach, it might be beneficial to go to that other station, rather than returning to Earth. Such an approach becomes critical if we have several large spaceships flying far from Earth - for example, on trajectory to Mars - and the crew from one needs to seek safe haven on another.
In total Mir had 28 main expeditions, keeping occupied continuously 10 years out of its 15 year flight. Mir was even targeted as a primary destination for space tourism. Conditions, including economics, weren't, however, right, and Mir was deorbited to South Pacific on March 23, 2001. However, the space tourism idea wasn't dead with the station...