I have to say it does depend on the personality of your toddler, dd2 was very compliant and wouldn't dream of letting go of the puschair, wandering off etc. Has long legs and would walk for ages. DD3 is a habitual escapee - absolute nightmare, dd4 is taking after her (unfortunately).
It also depend on how much car usage etc we walk a mile each way to school so unless they love the buggy board and will happily stay on it (dd2 was petrified of it and wouldn't go near it) then getting a 2 year old to walk (each way) would be traumatic. I rarely use my car live local to small town, supermarket, toddler groups etc so benefitted from having a double. Didn't get on with slings - I have a bad back and huge babies and I'm only petite myself - babies 10lbers.
What is your lifestyle like and what do you think it will be once baby arrives?