Depends at which hospital you want to deliver.
If you want to go to a private hossy - you have to fork out for an Ob. If you're happy to go public, no worries - totally unnecessary.
I've had one preg with and one without and Ob. Both high risk. With #2 I was allocated the best Ob they had and he saw me all the way through. Care I got was the same in terms of continuity, except the benefit with public was that you got to know the midwives who will deliver your bub and look after you post birth. With private you won't meet them until you go to the hospital in labour.
If the private room thing concerns you, you can always pay for priorty for a private room in a public hospital (for most that I've come across), but remember sick pts always come first.