oil attracts dust, wax repels, i would suggest wax on such a screen, of the two, but unfortunately i'm inagreement with your friend the pro, as to just leaving it be, neither is really necessary.
Wood does not "dry out" unless it unfinished and in a very dry climate or purposely put into a drying kiln to do so, there are "seasonal changes" of EMC [ equilibrium moisture content] that occur, with all finished woods, and that is the reason it is finished so as to protect if from quick changes in such as well as other things like spills, to beautify, etc.. But in an environment where the air is conditioned and heated with humidifiers and kept close to an average range of overall consistency, this is not a problem as compared to outdoor use of such is ok? There is no such thing as "feeding", or nurturing, the wood when finished, the finish either does it's job or it doesn't to what ever degree it can. Wax at most will give only a minor increase in protection unless applied to the end grain in a thick enough coating to protect from end cracking as it shrinks. As to your piano re finishers comments, it is possible for the sound boards that have less finish on them and if no installation of a humidity bar is in place, for them to dry and crack long before the case and rest would, but that is an exception to the rule. In either case no ones lying about anything, it's just a matter of circumstances of each pieces needs or un-needs. for the most part a good finish needs nothing else but dusting and wiping with soft cloths or dusters.
Bottom line, dust- save all the money you would spend buying oils or waxes or polishes and take your significant other out for some nice meals instead ok, lol