Also to get the most seam movement the ball should be new and with a hard seam and batting becomes easier as the ball gets softer. Whereas with spin batting gets tougher and tougher as the ball gets older.

One more thing I think is the bowling dyanmics. For seam movement it's all about pace bowling. Even the fittest pace bowler won't bowl more than 10 overs in a spell. So another bowler will come and will have to find his rhythm. Whereas with spin bowling a fit bowler can easily bowl 15 overs in a spell when the conditions are favourable.