Bogen, the minhag in America is that to meet the President, one would not wear a hat. So it would seem to be unnecessary. The Poskim seem to stress that it depends on the minhag hamakom, and a yarmulka is sufficient.
As far as a jacket, one probably would put on a suit and tie for the Pres, but few do for davening.
The poskim also say that in hot places, even short pants are fine, since that is what is normally worn. Some people find the heat of a jacket very bothersome, as well.
Finally, the gemara says that one of the amoraim would davka take off his jacket (shadi gleemaih) when he davened in an eis tzara, so as not to appear choshuv. It is more anivusdig to appear plain.
So as usual, if you are mechaven lshem shomayim, that is what really matters.