Does having participated in more number of contests have any impact on by how much the rating for a contest increases?
I don’t think your previous participation in contests matters much while deciding your delta for any contest unless it is your first contest. In your first contest, your rating is assumed to be 1500 and then your delta is calculated. Otherwise, it just depends on your current ratings and the current ratings of all the participants currently taking part in that particular contest.
You can read more about it here: Rating Mechanism | CodeChef