All my upgrades are with CR1s or 500 milers. I've not had a free upgrade in years, but I don't travel all that much (8-10 trips a year) and only on very popular routes. When I book on .bomb, I request upgrade at same time so as to be on the list early. With the 500 milers, I use a combination of earned & paid, so the additional cost is usually $100-200 per leg, which is worthwhile to me on a 5-6 hour flight (or longer if there is weather delay).

BTW, once I was on PS from JFK to SFO, and due to weather at SFO, we circled, then landed in Oakland, waited 2 hours for fuel and then had a 10 min flight to SFO. That was a bit over 9 hours on the plane total, and I was in row 9... and so very happy to have been there instead of Y.