AFAIK, spires were originally designed to help visually locate the church, from the days when people followed field paths through (more wooded) countryside. Putting bells there, if the church could afford to, supplied an audible signal not just of worship time but of irregular events like funerals and good/bad news. Not sure about the vents but probably to allow wooden beams etc to get air circulation.
Most public works projects, including churches, stone walls etc., built around this time were a form of social welfare i.e. providing jobs and wages to local men. You have to remember the 1840's were the height of laissez faire economic thought, and to merely 'hand out' charity to starving people was an anathema.