There's a few things happening here.
First, the Cold War had it's affect on people's minds. A lot of people simply can't imagine a Workers' State that doesn't degenerate.
Second, the Official TU is "plutocracy on steroids". The ability of a particular world to buck the system is limited, particularly if that world is just some random rock, rather than a optimally selected hi-tech, hi-pop world. (Hmm, that's a bit like what happened in the real world isn't it? Revolutions happened in dirt-poor or war-ravaged countries...) So the scope for workers' states to avoid degeneration is limited.
Having said that, in non-OTU settings, I have used reasonably functional workers' states. They are generally organised along the lines of the Paris Commune, or how the Soviets were _supposed_ to operate. Basically it's a huge federation of local communities, that becomes a confederation at interstellar distances. I don't pay too much attention to the economy, aside from noting the presence of highly advanced public services (health, transport and so on).
The PCs tend to have fairly standard backgrounds - there are other interstellar states out there, so there is a navy, army, (sometimes marines) and so on. There is interstellar trade, and this does involve some fairly small vessels that are effectively free traders of a sort. And of course, there is a Scout Service... which keeps an eye on what the neighbours are doing...
There are some constraints on the plots you can run - the true "merchant prince" campaign doesn't work too well - but generally you can run a pretty standard campaign, with a slightly different flavour.
Of course, the most obvious role for workers' state is as "evil empire". This can be a laugh when it turns out that they aren't so villainous after all. At this time, IMTU, it usually turns out that the Generic Space Nazis have been trying to incite a war between the Red Fed and the Yanks In Spa