I'd guess it really depends on what and how much you are making of different items. Considering that smoking is typically a much longer process than steaming, and far messier and requires significant ventilation, I'd probably be more concerned with the smoking than the steaming.
No room for a countertop steamer? You could almost certainly get a quallity smoker and a quality steamer (or combi oven) for the price of the combi oven/smoker/steamer...those things look ridiculously expensive.
Are there other methods you can utilize to make the things you are wanting to steam? Would you be concerned about getting some smokiness into the things you are wanting to steam? A little smoke flavor on some rice or some veggies might not be a bad thing...so the issue of residual flavors in the combi oven might not be a real issue.
What about setting up a smoker outdoors? Would that be a possibility given your location and health code requirements?
Is there an indoor location aside from the kitchen that would work for either the smoker or steamer? An indoor smoker would need ventilated, but might not need under ansul or under hood depending on your local codes and the smoker used. An indoor steamer probably doesn't need to be under hood or ansul, so as long as the location its in is sufficient for health code purposes and you can get a cold water line to it it should be ok.
Probably what you would want to do is sit down and chart out all the things you are wanting to produce, the methods to produce them, the time involved, and any alternative methods of producing them. Basically, take stock of what you are wanting to do. Then look at the resources you have...space, time, money, labor...which ones you are short on and which ones you are long on. Then figure out how to best use your resources to produce the things you want. Maybe this means finding a different method of cooking something to fit everything in. Or taking something off and/or replacing it with something else. Or purchasing a piece of equipment you haven't quite considered yet, or going ahead and getting the combi smoker. Or restructuring your scheduling to get certain things made at different times.
All in all I'd probably be more concerned with having a quality smoker than worrying about a steamer. The time and labor saved with a commercial smoker vs pulling out a bradley would be immense. And unless theres some very specific things you are wanting to steam that just can't be done any other way, you can probably find a substitute method of cooking for the steamed items, or just jury rig something on the range or in the oven for when you need to steam. With smoking its nowhere near as easy to do that, given the cook times involved and the issues of ventilation, cleanliness, and maintaining smoke and temps (especially for cold smoking). So given the difficulties involved with smoking vs the ease of steaming I'd be much more concerned with having a good commercial smoker than a steamer or combi.