The saving is only as valuable as the time left on the mortgage. A low rate with four years remaining is worth far more to a buyer than the same rate with fourteen months left, since Canadian mortgages compound semi annually and the benefit ends when the term does.
For a seller, a rate that low widens the pool of interested buyers rather than raising the benchmark price for the street, since a buyer's lender still has to approve the assumption and qualify them under normal underwriting.
Treat the assumable rate as one selling feature to arrange early with the lender, not as a number that changes the home's appraised value. Get your hand-reviewed valuation from Joel Dyck.