[taranaki]

Promotions are not awarded for the benefit of employees. They are usually awarded because the employer believes that he/she can extract a safer return for the wage bill by promoting internally than by hiring an outsider for a senior role. Better the devil you know,etc.
No doubt there are extra responsibilities that go with the new position. Any pay rise that you receive will reflect the company's higher expectation in return. I've worked with a large company for long enough to realise that the higher up the ladder you climb, the greasier the rungs get. When the going gets tough, the guys in the middle generally get shot before the top or the bottom.
Good luck with the promotion, you must have the qualities and atitude that those upstairs think neccesary to achieve their objectives. Save the letters of gratitude for when they drop you an unplanned cash bonus or some other random act of kindness. Nobody gets moved unless the boss sees potential to maximise his return on the wage dollar.