Impossible to say, really, and what stance a scholar takes on the issue can often be a bit of a tell for their attitude on empire in general. Someone wanting to say that it wasn't profitable might emphasize that it was relatively poor and has a restive northern frontier, those wanting to emphasize it's profitability might mention it's metal resources and later productivity of products like wool. But we sinking do not have close to the data necessary to make a responsible judgment.

I will note that the discussion tends to proceed along oddly mercantilist lines, as a matter purely of resources gained and a favorable import export balance. From a neoclassical perspective the conquest of Britain removed substantial barriers to trade, and this has support from the ample archaeological evidence of a vigorous trade network encompassing Britain, the Rhine delta, and northern Spain and France.

As for ancient attitudes, the evidence is problematic. Tacitus portrays it as a waste, but that is part or his political criticism and this Britain in and of itself isn't really the point. A couple centuries later, someone wrote a speech in praise of Constantius, who put down a rebellion in Britain, by describing the island as vital and very wealthy. This too is clearly not very trustworthy.