Baro-aiding is really only useful in the navigation solution itself. The altitude (or elevation) data provided by the airborne receiver is a "raw data" value that is, in itself, quite unreliable. It is possible to obtain survey quality elevation data, but this requires DGPS survey, followed by subsequent "massaging" of the data to account for errors in SV positions, among other errors.
And, of course, a correcyion must be applied to the assumed WGS84 spheriod, to be able to relate it to the real world earth.
AFAIK, Airborne receivers aren't (yet) capable of taking those extra steps that will yield an accurate elevation, thus the altimeter will be needed for another few years... or so...