Hi Tom.
On the one hand, you could get it, as it can be picked up rather cheap now too.. And there's a lot of fun to be had with it, that's for sure.
But on many points SS08 has improved a LOT, compared to SS06, so you might find yourself playing SS06 and missing a lot of features or options, and this might be a little bit dissapointing too. I found myself playing it less and less, since SS08 is just the better one (obviously).
I cannot really tell you what to do of course, but if you're a fan of the sim, and have a few quid to spare, it will certainly keep you entertained for quite some time, if you can ingore the fact that it lacks SS08's features in some area's.
It does have some unique ships that did not make the transfer to SS08, so that's got to be worth something too I reckon. So in that case, I'd recommend it, yeah.
Fred