The dust and smoke is a deal killer for some. The only way I have heard of reducing/removing smoke is either a water tray or a
very large dust collection unit. I suppose if you had two cutting tables, one with metal suspended over/in a water table, and another table for wood only, then you could get by with a "dual purpose" machine. You would have to design the cutting rail system to be mobile, and move over each separate cutting bed.
Although that would entail you building most of the machine, and I don't know of any manufacturer that would sell something like that....
or you could try your hand at a very big and nice dust extraction unit. I would be concerned about how long any fans or vaccuum units would last, as the plasma dust is pretty abrasive. That is the situation you are in. The tool change over sucks at the very least, but it is not half the problem that the resulting mess is. Wood dust + plasma sparks = bad (where I come from).
I would say that there are a number of choices out there for a decent plasma table, including building your own, though this is not for everyone.
Torchmate, Trackercnc,Dynacnc,Dynatorch,EZrouter,Practical all make a machine, I would search the threads on this site for feedback, good and bad, about each. There are a number of other machines out there in the "small industrial" size, but don't crucify me for not thinking of them offhand
Now, as far as cut quality, most signs I have seen are no thicker than 11 ga, if that. I doubt that you will see any poor quality edges or cuts on metal that thickness or thinner. I have some 3/16 tabs I cut, right next to some 3/16 tabs cut with a laser. The cut quality is negligible.