I agree 100%.
I would be all for having Navarro back, as long as it doesn't mean we cant, for example, make another move for SP. If the money is an issue then they may need to get creative with the position.
He's probably one of the better if not top backup catchers in the league, and would be an average (or maybe below average) starter. If he can get a contract from a team wanting him as a starter then maybe we can't keep him. It would be a huge depth signing, because I want to puke at the thought of Thole being the starter if Martin gets hurt.
Also, if the Jays are willing to pay him 4-6M a year as a backup and that's what teams are offering him as a starter, why not stay with a contender and limit your playing time, reducing the risk of injury and prolonging your career? At this point in his career I don't think he's inline for a big, multi-year contract, so taking 1-2 years for 10-12M is probably all he will see.
The only real downside to resigning him (if possible) is that Martin catches Dickey for another year, and the money it would cost to keep him. However, I think I would prefer those downsides to the possibility of Thole catching if Martin gets hurt, or even just having Thole in the lineup every 5 games.