as zerocrossing already stated it's mostly about character and what inspires YOU.
soft synths nowadays can sound pretty much indistinguishable from the hardware they emulate and at least for the more bread and butter side of things, can sound even better (or worse) than the original, simply based on what kind of nuances one prefers and not, what is factually better.
There's been a blind test on Gearslutz very recently, where Diva (while still being a totally awesome sounding instrument, it's generally not anymore seen as the pinnacle of analog sound emulation on it's technical side) was put up against a Behringer Model D and i think 2/3rd of the people picked it wrong. Many (myself included) even preferred what was later revealed as Diva footage.
i also agree with him that for the most part, as of yet, emulations do not capture the more extreme side of analog - like the ‘effortless/smooth‘ sounding overdrive/distortion that happens naturally on analog hardware, that mostly happens in software only if you tack on a dedicated saturation/distortion algorithm. Digital can also give great results, but it usually doesn't sound like what i'm used from the analogs i have. Same applies to extreme filter FM.
Having said that, i don't use Diva (even though i really like it's concept, i can't get along with it's user interface which doesn't inspire me one bit), Repro, or Moog emulations as i've found other synths that give me more the sounds i'm after.
Which- again is more because their generally characteristics suit me better and not because they have ‘t3h m0st @nAL0g s0undz evor!‘
regarding the viability of an OB-6 vs softsynths. It is - again - a matter of personal preferences, including it's characteristic sounds.
If you don't hear anything that's particularly pleasing you, you simply don't need it.
It also doesn't have to be ‘high end‘ or high price tagged. If the sound of a Microkorg, a Monotribe, Z3TA+, or PG8X inspires you, they can be of more musical value to you, than even the most expensive synths on the planet, which actually might not give you that sound / user experience / satisfaction even if you can afford those.
With expensive hardware, you hopefully also get a quality keybed. The user experience can be more satisfying (a ‘true‘ tactile instrument vs a more visual and mouse click dependent workflow), it will still work (or remain readable
) regardless if you upgrade your computer, has zero latency, will give different results due to a different user experience, can be the pride of your studio (though the latter could of course also apply to any software if you prefer that)