An unpermitted suite narrows rather than widens the buyer pool. A lender will not count income from a suite it cannot verify as legal, so a buyer financing the purchase as a single-family home gets no credit for it, and an investor buyer will simply price in the cost of legalizing it later.
Buena Vista's mid century housing stock includes plenty of these long-standing basement or upper suites added over decades, which means the paper trail on any specific property varies house to house rather than following a neighbourhood-wide pattern.
Confirming that status before listing is the difference between pricing the premium and pricing a renovation project. Get your hand-reviewed valuation from Joel Dyck.