Are members who join with a price incentive more or less likely to renew membership the following year?
Less likely. Don’t offer pricing discounts unless your audiences are EXTREMELY price sensitive or your membership is declining and you’re desperate to get people in the door by any means necessary.
Does offering a discounted membership based on time of the year (i.e. a summer sale) dilute the value of membership?
Yes. Also, when you start offering discounts, you train your members to bad behavior: “Well, I waited to renew last year, and they offered a discount, so I’ll wait again this year and see if I can get another deal.”
Now that’s different than pro-rating membership when everyone’s renewing on the calendar year. If a new member joins in July, one school of thought says “charge that member 50% of your regular rate,” but I’m not a fan of that because then that new member is going to start receiving “it’s time to renew!” notices almost immediately. I encourage clients to offer “18 for the price of 12.” That is, the new member pays the full rate NOW, but isn’t solicited to renew until next year’s renewal cycle.