I have been upgraded on KLM intra Europe and also intercontinental KLM flights by KLM frequently.

I have been a KLM RoyalWing elite for about 6 years now, although recently slipped to SilverWing, and I have never bought anything other than the cheapest fare possible.

Generally it has been when I've had an overnightin amsterdam and so had to checkin for my onward connection.
On the AMS to LIS route I would say my upgrade rate is about 3 in 4

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Continental Airlines
KLM Royal Dutch Airlines
NorthwestAirlines