Data Point:

I hold a BMO Airmiles Gold card. I upgraded it from a non-fee airmiles in October to get the 2,000 airmiles. I spoke to the CSR rep today who was prepared to do a product switch (no-credit hit) to the World Elite. He said I was eligible for whatever promotion is online right now. (FYF and $300 credit)

I have held that account for 15 years, but just keep switching between cards.