The 105/2,5 is an uncommon lens. In my opinion it should not be put in competition with other lens models.
It is a rather sharp lens when stopped down to f/4 (but for instance the 180/2,8 ED seems sharper to me) but its real specialty is in the extremely, should I say perfectly, smooth gradation from sharp to unsharp areas. This characteristic in my opinion gives a special look to images of tri-dimensional objects, such as portraits and even landscapes. Nice rendition of out-of-focus and nearly-in-focus areas often makes images taken with this lens look sharper, or at least nicer, than images taken with sharper lenses with less good bokeh rendition.
One should try to take portraits with this lens at f/2,8 focousing precisely on one eye of the subject. This will give a sharp, lively eye and brows detail, with soft, silk smooth hair.
Good used 105/2,5 can be easily found and bought for very cheap money. The lens is simple and sturdy, and if choosen with some attention it will probably outlast its buyer. Even bought new the 105/2,5 will provide a super performance, unbeatable in some occasions, for its price.
A 105 micro, or similar lens, with a "soft focus" add on will never replicate this kind of performance. Nor will a more complex "hyper sharp" lens with a less perfect sharpness gradation. Maybe the Nikkor AF 105/2 DC can simulate the performance of its predecessor, but a multiple cost and with much more volume and weight that the slightly higher speed does not compensate.
I also use a 180/2,8 ED, an Elmarit-M 90/2,8 and a Tele-Elmar-M 135/4. Super lenses each of them, superior in some areas, but can not replicate the Nikkor 105/2,5 performance.